Final Report Summary - SINERGY (SILICON FRIENDLY MATERIALS AND DEVICE SOLUTIONS FOR MICROENERGY APPLICATIONS)
Executive Summary:
Energy autonomy keeps being one of the most desired enabling functionalities in the context of off-grid applications, such as continuous monitoring scenarios and distributed intelligence paradigms (Internet of Things, Trillion Sensors). SiNERGY has focused on silicon and silicon friendly materials and technologies to explore energy harvesting and storage concepts for powering microsensors nodes. Harvesting energy, tapping into environmentally available sources such as heat and vibrations, may be a good powering solution in man-made scenarios applications. 10-100μW/cm2 power densities seem appropriate for many such applications. Coupling those harvester devices to secondary batteries to buffer enough energy to account for the power demand peaks required by wireless nodes would be an enabling energy autonomy solution.
SiNERGY has selected relevant examples of power microgeneration and storage (thermoelectric generators, mechanical harvesters and microstructured batteries) pushing them further into their performance and development maturity. Emphasis has been placed on thin films and nanostructured materials and their integration into mechanically and thermally optimized microstructures. For bringing the eventual solutions closer to an exploitable phase, silicon technology compatible materials have been considered. Silicon micro and nanotechnologies provide an enabling path to miniaturization, 3D architectures (improved energy densities), mass production with economy of scale, and the possibility of easy integration with other microchip based devices (sensors & actuators, power management circuits, communication units...)
Silicon friendly materials and device solutions for thermoelectric harvesting. Thermoelectric microharvesters able to convert heat flows into small, yet high added value, amounts of electric power have been pursued. The activity has focused in successfully integrating silicon nanowires as low thermal conductivity material into devices with optimized thermal and electric design. Both, bottom-up and top-down approaches for nano-objects integration have been explored.
Silicon friendly materials and device solutions for mechanical energy harvesting. Electrostatic and piezoelectric harvesters have been explored to convert small vibrations into a useful power. In the first case, an optimized silicon based electret material has been integrated in a robust laterally moving microstructure. In the second, the integration in vertically moving microcantilevers of a piezoelectric composite based on ZnO nano-objects has been attempted, and a hybrid fabrication approach combining silicon and printing technology has been shown promising.
Silicon friendly materials and device solutions for solid-state microbatteries. Material and interface optimization (from a fast charge/discharge perspective) has led to the fabrication of a functional thin-film planar microbattery for on-package energy storage. Translation of this knowledge into 3D microbatteries, fully compatible with Si technology, for increased capacity and power has been attempted. Failure to identify a good solid electrolyte has prevented full success, but a hybrid 3D battery has been assembled.
Integration feasibility. Even though SiNERGY focuses in materials and technologies, attention has been paid to real applications. As a consequence, system integration issues have been tackled at different levels for the above microenergy devices. A gas fryer scenario has been explored for the deployment of thermal harvesters, piezoelectric devices have shown appropriate for powering remote nodes at useful duty cycles (e.g. for preventive maintenance), and the electrostatic harvester has been shown functional in a Tire Pressure Monitoring application.
Project Context and Objectives:
SiNERGY in a nutshell
The project addresses the development of energy harvesting and storage devices suitable for solving energy autonomy issues of unwired powered devices working in low-power and/or pulsed regimes that will be required in continuous monitoring scenarios. The combination of an energy harvester with a small-sized rechargeable battery is the best universal approach to enable energy autonomy in those applications.
The microenergy elements of interest for SiNERGY are then harvesters and solid-state batteries. In the case of harvesting, thermoelectric and mechanical harvesters have been considered given that temperature differences and vibrations are the most common environmental energy sources in manmade scenarios. The focus of the proposal is placed on the microdomain to obtain small size devices with high energy density features, and on the silicon technology friendliness of materials (and approaches) to assure the eventual manufacturability, integration and cost effectiveness of the related devices/solutions.
When resorting to silicon technologies, the material issue cannot be dissociated from the architectural issue, which unavoidably brings the focus closer to the device level. This is an added value because the development and exploitation of the devices is moved one step further into maturity. For this reason, not only different low dimensional material options (crystalline and polycrystalline Si nanowires, Si-Ge nanowires, ZnO nanoobjects, and oxide, nitride and metal thin-films) are considered, but also different technological fabrication approaches (bottom-up or top-down approaches), and device architectural alternatives (micromachined thermally isolated platforms, micromachined in-plane or out-of-plane movable platforms).
The high volume, cost-effective and sustainable fabrication enabled by micro and nanotechnologies will support the advent of energy autonomy solutions required by the eventual success of numerous applications. Three of these applications have considered as a frame of reference for our developments: tire pressure monitoring systems, smart cooking appliances (as an example of machine condition monitoring), and generic preventive maintenance. As a test case, each presents a different harvesting scenario: vibration in the first, hot surfaces in the second, both in the third (always it will be used for vibrations in our case) and a different motivation for going into the microdomain (physical space constraints in the first and the second and multiplication of nodes in the third case).
SiNERGY context (1): microenergy vs macroenergy
We are talking here of microenergy, tiny bits of energy and a few microwatts of power, not of the 10^16 TW that yearly are produced worldwide. Society of today needs abundant energy to power our cars, factories and homes, but society of tomorrow will also need abundantly distributed energy to power the billions of sensors that will be deployed in the Internet of Things to come.
We are not referring either to ‘microgrids’ (which is an abuse of language for designing locally redistributed macro energy sources). We use the term micro to really refer to miniaturized cm-size devices. Silicon technologies are the techniques of choice in SiNERGY. Other large volume, cost effective technologies exists that are also miniaturization-prone to some extent, such as lamination or printing technologies. They even excel over Si Technologies when producing cheap large area devices or flexible devices, but Silicon technologies are the ones better situated to obtain devices with internal micro and nanofeatures. If the Internet of Thing is going to bring us billions of sensors, they will be probably small, and, consequently, the harvesters/batteries supporting their energy needs should also be small. However, the only way of capturing enough energy from low density harvesting sources with such small devices is that those devices have high internal features density (for instance 3D internal architectures where to integrate large surface-to-volume ratio nanomaterials if need be). Silicon technologies are also the only ones producing (by means of micromachining) small scale free surfaces and volumes that allow those devices to effectively couple to environmental stimuli.
SiNERGY context (2): off-grid energy autonomy
As we know, off-grid energy autonomy is one of the most demanded functionalities since it enables a wide range of interesting disposable, portable and deployable applications. In all these cases, energy is usually provided by batteries. SiNERGY focuses in deployable solutions, where periodic battery recharge or replacement will be unpractical when faced with such a large number of devices.
Energy harvesting, tapping onto environmental sources of energy, such as vibrations or waste heat, can be a way of directly powering the sensors, or keeping continuously charged an auxiliary battery that will be a pretty universal energy autonomy solution.
SiNERGY objectives
Thermoelectric harvester
Since waste heat is one of the most recurrent environmental energy sources, one of the harvesting options considered is the development of a thermal microharvester, which given the philosophy of SiNERGY will be attempted using silicon technology friendly materials and architectures. High density features are needed to overcome the trade-off of silicon being an enabling technological material but a poor/modest thermoelectric material
The main objective, for this purpose, is:
• the integration of silicon based nanowire (NW) arrays as thermoelectric material into a silicon micromachined structure. This structure shall enable an internal thermal contrast to develop between two isolated silicon regions, which once bridged with the Si NWs, will be the basis of an all-silicon microthermoelectric generator.
Intermediate objectives for achieving this goal are then:
• Obtaining high density arrays of (arbitrarily) long nanowires at wafer level, considering different bottom-up and top-down synthesis/definition processes
• Obtaining a microstructured platform with compact quasi three-dimensional features with two distinct areas of thermal contrast, one in contact with the silicon bulk, the other in contact with a microradiator to be integrated on top.
• Devising a fabrication technological route that makes compatible the integration of above three elements (Si NWs, microplatform, microradiator), and enable power output densities in the 10-100 μW/cm2 range
• Avoiding the use of extreme lithography / nanolithography in the process sequence, thus decreasing the technological complexity and cost of the resulting devices and easing their large-scale replication
• Choosing an architectural arrangement in which the arbitrary long, high density nanowires arrays are integrated in the microstructure platform in a way that good thermal and electrical connection is assured at no extra technological cost.
Mechanical energy harvester
Another possibility of energy harvesting is using mechanical energy, e.g. vibrations. There are three main methods to convert mechanical energy into electrical energy: electromagnetic, piezoelectric, and electrostatic. For many small autonomous sensor systems, miniaturisation and cost effective manufacturability are important requirements. Silicon technology is the way to go to reach those requirements, but this rules out the use of electromagnetic transduction - It turns out to be virtually impossible to efficiently scale down and integrate pick-up coils and magnets into silicon technology.
Therefore, SiNERGY focuses in:
• Developing electrostatic as well as piezoelectric energy harvesters based on Silicon technology with high power output and good reliability.
Intermediate objectives to achieve these goals are:
Electrostatic energy harvester:
• Material development and optimisation for silicon-based electrets (the polarisation source for electrostatic energy harvesters).
• Integration schemes for these electrets, with high surface voltages and long charge retention times (10 years @100°C) into out-of-plane mass-spring MEMS platforms.
• Device optimisation with increasing capacitance variation and minimizing parasitic capacitance. The power output goal for the electrostatic energy harvester is 500 mW for 1cm2 area.
• Reliable devices with shock resistance up to 5000 G.
Piezoelectric energy harvester:
• Fabrication of out-of-plane cantilever type Silicon MEMS structures
• Adaptation of compatible MEMS processes for reliable synthesis and integration of piezoelectric ZnO nano-objects onto silicon microstructures
• Device design which optimizes the strain/stress of nano-objects under short displacement vibrations, in order to achieve power densities beyond 25 mW/cm2
Solid State Li-ion microbatteries.
For the application of autonomous systems powered by harvesters, on-board energy storage devices are required to ensure a stable current supply and cover peak demands. In particular, lithium and lithium ion batteries (LIB) have the highest energy density of all known systems and thus represent the best choice for rechargeable batteries. Since liquid electrolyte based batteries present safety issues and limitations in size and design, pure solid state devices are gaining ground particularly for miniaturisation.
The main objective of this project is to develop high performing thin-film all-solid-state lithium-ion microbatteries compatible with silicon technology. In order to significantly increase the power density and capacity of the State of the Art microbatteries, a double approach based on improving kinetics of ion transport at the interfaces and increasing the effective surface area will be followed.
Two different architectures will be developed in order to face up the main goal of the project, namely:
• Thin-film planar structures to specifically implement strategies for improving ion transfer at the interfaces, i.e. current density, by multilayer deposition of all-based spinel microbatteries.
• Three-dimensional geometries to increase the current density, power capability and energy storage capacity by simply increasing the surface area.
In the planar configuration, performance will be the main target measured in form of rate capability (power) and lifetime (cyclability). In the 3D configuration, emphasis will be put on battery capacity (energy-density) and issues of mechanical integrity (reliability).
Intrinsically linked to the development of these two architectures, intermediate objectives of the project can be listed as follows:
• Deposition of defect-free thin-film electrolytes with high-enough ionic conductivity and reduced thickness (low internal resistance).
• Deposition of crystalline multilayers (cathode/electrolyte/anode) all-based on the spinel structure with continuous and smooth interfaces.
• Microfabrication of high density three-dimensional structures based on dry etched Si pillars fully compatible with silicon technology.
• Deposition of high quality conformal electrolyte/electrode multilayers (to be applied in 3D structured substrates).
Project Results:
Si NWs based micro thermal harvesters
Bottom-up approach
The bottom-up approach is based on the integration of arrays of Si NWs as active material in a previously fabricated Si microplatform able to endure the hard requirements of NWs growth process (high T). During SiNERGY project the efforts have been focused on the optimization of both elements, with the aim of increase the harvested power per unit area and accomplish the requirements foreseen for powering a wireless sensor node.
Si NWs optimization
The first goal in Si NWs development was the reduction of the high temperature required for the growth process, so as to limit the suffering and potential breakdown of Si microplatforms during the NW integration step. This was attained by changing the chemistry of the VLS process used for NWs growth, moving from silicon tetrachloride (SiCl4) to silane (SiH4) as silicon precursor gas. Process temperature was reduced from a 750-800ºC range to just 630ºC. The process was completed with the addition of diborane (B2H6) for ex-situ doping of the NWs and hydrogen chloride (HCl) to prevent the deposition of added polysilicon thin films.
Galvanic displacement method used for selective deposition of Au nanoparticles in bared Si walls (vertical <111> planes in trenches) was totally revised to allow a tighter control of nanoparticle size, the key parameter governing NWs diameter, and, therefore, overall array resistance. A comprehensive study determined how to use different process parameters to obtain statistical control of nanoparticle size distribution and deposition density. Cumulative count of NWs shows that mean diameter is 113 nm, and 80% of NWs have diameters between 76 and 207 nm; areal density of about 1 NW/µm2 is obtained with this optimized process. The required pre- and post-processes involving wet steps were adjusted for suitability with new microplatforms.
A complete set of test structures, and specific measurement methods were developed to determine the material properties of NWs. Electrical and thermal conductivity and Seebeck coefficient were measured making use of ad-hoc test structures for single or several NWs. Values obtained, 200 S/cm for electrical conductivity, 6.5 W/m·K for thermal conductivity and 331 μV/K for Seebeck coefficient result in a figure of merit ZT≈0.11 for Si NWs used as thermoelectric material in bottom-up based μTEGs, obtained with NWs with a 113 nm mean diameter. This ZT value exceeds that of bulk silicon by a factor of 10 and is the first reported for Si NW arrays epitaxially integrated in micro-thermoelectric harvesters. The thermal conductivity was determined with a novel method based on thermal AFM and fitting to a thermal model.
Si microplatform optimization
The key goal in the development of Si microplatforms was the improvement of the thermal isolation between hot and cold parts to boost the thermal gradient obtained from a waste heat source. New designs implemented in SiNERGY kept the use of successive trenches to attain a longer effective NWs length between hot and cold parts, and introduced a new type of low thermal conductivity supports for the metal lines. In this way, after Si NWs integration, microplatform parts are linked only by thermocouple active materials, avoiding other parasitic heat paths. The designs adopted for these parts allow arbitrarily long features, which can be dimensioned to the optimal values required by the Si NWs properties.
The Si microplatform fabrication process was revised to enhance power levels provided by μTEGs. The metallization and the metal-Si contacts were improved in order to not degrade the low internal resistance provided by the dense Si NWs arrays (large amounts of highly B doped Si NWs connected in parallel). TiW was selected for electrical interconnections, using a preceding boron doping step and a subsequent thermal annealing process to ensure the formation of a silicide layer in contact areas.
The thermal contact with the environment (heat removal in the cold side) was identified as the key limiting factor in performance. A process was envisaged to fabricate a thermal interface structure in current devices, linking the isolated suspended platforms with a standard metallic thermal heat dissipater. Although integration was not yet accomplished, conservative estimates show that demo application power targets can be attained using a reasonable device area (a few cm2 at most).
Other advances adopted in the course of SiNERGY project, both on the design and fabrication of the Si microplatforms, were intended to increase production yield. The platform robustness was enhanced using thick Si bars to hold the suspended platform in the most critical phase, i.e. before the integration of the Si NWs. The membranes supporting the metal connections were redesigned to match with square apertures for the DRIE in the backside, leading to a steadier etch process. The passivation thickness was increased and a partial etch was performed in bond pads location to avoid the exposure of whole metal surface after NWs integration. Finally, the whole fabrication sequence was rearranged to avoid the critical interferences between the different micromachining steps involved.
µTEG performance
The integration of improved bottom-up Si NWS into silicon micromachined platforms was achieved, and harvested power with resulting μTEGs was assessed in different conditions. Measurements performed in still air show low thermo-voltages (hundreds of μV) comparable to the Seebeck coefficient measured for Si NWs arrays. Thus, in this condition the delta T achieved from the hot surface is in the 1-5 °C range, resulting in quite low harvested powers (10 nW. Therefore, the integration of a heat exchanger seems to be mandatory for having efficient devices. However, measurements performed using forced convection to emulate the effect of a heat exchanger provide a delta T in the 10-40 °C range, still lower than values attainable with a passive heat exchanger according to simulations).
Data obtained with forced convection (showing a voltage increase of 8 times when compared to still air), allow the estimation of the power expected from such devices in realistic operative conditions. The 2nd generation best samples show maximum generated powers around 0.07 µW from a device surface of 4 mm2 (1.75 μW/cm2) with open-circuit voltages around 3 mV, obtained with a hot-surface temperature of 120 °C. Thus, the ≈ 10 µW target needed for practical application on demo scenario can be basically reached with a device area of 2.5×2.5 cm2.
Future development
Despite the appropriate results achieved with the bottom-up μTEGs developed in SiNERGY, in line with the power requirements agreed for an autonomous wireless sensor node, there is still room for performance improvement. Future efforts will be focused on the integration of proposed heat spreader element in current microplatforms, in order to remove heat from cold parts to the ambient and procure a higher delta T from available waste heat sources. The design of the microplatforms can also be optimised in terms of power density, which in current devices was waived to allow the integration of the self-test heating element. There is also room for improvement of the active material ZT. Work will focus on a further reduction of the NWs diameter to approach the 50 nm target, to get an extra reduction of NWs thermal conductivity. Other active materials with potential better thermoelectric properties, like the SiGe, will be investigated to be used with the bottom-up VLS growth process. This activity will be conducted in the framework a national research project recently granted by Spanish Ministry of Economy and Competitiveness.
Top-down approach
In the top-down approach, lateral architectures (using silicon NWs) were obtained. Lateral thermoelectric harvesters were designed to be fabricated in stacks, enclosing LPCVD grown poly SiNWs within a SiO2/Si3N4 mould. Heavily doped p- and n-type polysilicon legs were fabricated. Multilevel arrays of such NW (pairs of 3 level stacks) were closely packaged (separation of about 300 nm).
Tests were carried out on to evaluate the yield of the manufacturing process and the thermoelectric properties of the fabricated nanostructures. In the first-generation top-down devices the electrical resistance was found to scale correctly with the number of nanowires in parallel. Moreover, from the measurements, resistivity values were found typical of the high-doping range (around 1020 atoms/cm3) required for high-performance thermoelectric conversion. Specific test structures were utilized to estimate the Seebeck coefficient of the n and p-type NWs. An approximately linear growth of the Seebeck voltage with the temperature difference was obtained. The Seebeck coefficient of the nanowires was around 150 µV/K for both doping types, as expected considering the high-doping level of these nanostructures.
Simulated tests of operation were also carried out using a hotplate to check the produced thermoelectric voltage in conditions close to the real application foreseen for the devices, using a commercial radiator fixed using a special double-side adhesive tape sold with the radiator. Devices appeared to promptly respond to the temperature variation, with produced voltage in the order of 300 mV for heating temperatures as low as 80 °C.
The weak point of the first-generation devices was the fabrication yield, showing a critical at the wafer-boding step. However, numerical simulations showed that the performance gain using vacuum packaging was significant only for NW stacks with a high number of levels. On the contrary, for stacks of nanowires composed by a reduced number of levels, the performance of the device working in air can be comparable if not better than the vacuum packaged devices. This enabled a major simplification of the manufacturing process. The process flow could be modified by replacing the wafer bonding procedure with a plain SU-8 lithography followed by a backside etching of the entire thickness of the substrate up to the membrane constituted by Si3N4, SiO2 and by the nanowires. This made the dielectric membrane containing the nanowires more robust, allowing to mount on it a metal heat sink. A commercial anodized aluminium heat sink could then be fixed manually on the suspended masses, achieving high fabrication yields.
The conversion rate of the second-generation top-down devices was tested under simulated operative conditions. A maximum generated power around 0.16 µW from a total device surface of 0.64 cm2 (0.25 μW/cm2) with an open-circuit voltage around 3 V was obtained at a hot-sink temperature of 120 °C. Thus, the target of ≈ 10 µW needed for the practical application on the demo application is basically reached with an exchange area of 6.3×6.3 cm2, also considering that the modification of the doping process for n-type nanowires allowed to obtain a ≈ 10× reduction of the electrical resistance of the devices.
Mechanical energy harvesters
Electrostatic approach
Layout, materials and process flow of the 1st generation electrostatic devices
The basic configuration of an electrostatic energy harvester consists of five key elements: a seismic mass, suspension/springs, a set of electrodes, a charged electret and a packaging. We chose an in-plane sliding capacitor with a large usable mass and electret/electrode area and thus potentially the largest output power.
The active part of the harvester consists of a variable capacitor, created by two sets of interdigitated electrodes on the bottom glass wafer (W1) and the charged, patterned electret on the Si wafer (W2). This ensemble is sealed with a top glass wafer (W3). Upon movement of the mass, the overlap (capacitance) changes periodically, resulting in a generated AC output voltage. The flexible springs allow for an in-plane movement of the mass. The micro-fabrication possibilities in bulk silicon, together with its high stiffness and low susceptibility to fatigue, make Si the ideal material to fabricate the springs. The mass and the spring system can therefore be integrated in the one Si wafer. Important for the long term functioning of the harvester is the stability of the electrostatic charge on the electret. We chose for an inorganic SiO2/Si3N4 layer because of the good charge retention and for patterning of the electret by pre-structuring the substrate by DRIE prior to the deposition of electret layer. This has as major advantage that the nitride layer is continuous, which eliminates the possibility of charge diffusion.
Apart from carrying the capacitor electrodes, the packaging has different functions: first, it provides protection for the (fragile) Si mass/spring structure, limiting the out-of-plane mass displacement and therefore increasing the reliability. Second, in case of a hermetic vacuum packaging, the lifetime of the electret is extended by excluding influences from moisture and third, the vacuum eliminates the power loss due to air damping during mass movement. We chose to use a wafer-scale adhesive bonding process, where in case of the W1-W2 waferbond, the structured adhesive polymer also defines the capacitor distance. A stepped dicing process allows access to the electrodes on the bottom wafers. The 1st generation devices were successfully produced via the described route. The output power of the devices was measured using a shaker setup with sinusoidal input vibrations, showing the characteristic resonance curves of output power versus frequency, and a quadratic relation between the output power and the input acceleration. The maximum generated output power was in the order of 600 µW for an input acceleration of 3.5 g (maximal mass amplitude) at a resonance frequency of around 1100 Hz.
Improved 2nd generation electrostatic energy harvester layout and process flow
Although successful in terms of output power, the thin silicon springs of the 1st generation devices were mechanically not robust enough for the targeted application in a TPMS. Improving the mechanical reliability was therefore the main point for the 2nd improved device generation, to facilitate the ease of integration in the TPMS. The most important changes in device layout and process flow were:
- Integration of the flexible silicon stoppers to improve the shock resilience. These could be integrated in the device layout using the two existing DRIE steps for the Si wafer (electret etch and spring etch) without adapting the processing.
- Integration of cavities with dimples in the capping wafers, reducing the out-of-plane movements of the mass, while maintaining the freedom of movement.
- An improved waferbond between the bottom capping wafer with electrodes and the Si device wafer with the electret: replacing the lithographically patterned thick BCB bond polymer by a thin layer of SU-8 around the cavity in the capping wafer, results in an increased bond strength (reliability) and simultaneously improves the hermeticity of the device, providing a better vacuum (output power) and moisture barrier (lifetime).
These proposed layout and processing improvements were all successfully implemented during the fabrication of a batch (5 wafers) of 2nd generation electrostatic energy harvesters, resulting in a high yield and devices without visual errors.
2nd generation electrostatic energy harvester device characterization
Devices mounted on PCB were characterized on the shaker setup sinusoidal input vibrations and the output power was determined using the generated AC voltage signal, as well as in DC mode by charging a storage capacitor after rectification. The devices showed a power output of up to 700 µW at 0.5 g input acceleration. While this level of output power was comparable to the 1st generation devices, the low input acceleration necessary to obtain this, is remarkable. Due to the high vacuum SU-8 waferbond, the energy loss due to air damping was reduced and the sensitivity of the 2nd generation devices increased dramatically (3000 vs 50 µW/g2).
For a more application oriented characterization, band-limited white noise with a PSD in the range of what is to be expected in a car tire (10-4 to 10-2 g2/Hz) was used as input on the shaker system. The generated output power increased from 30 µW for the 1st generation devices to almost 200 µW for the improved 2nd one.
In conclusion several reliability improvements were integrated in the layout and in the process flow for the 2nd generation electrostatic energy harvesters, leading not only to mechanically robust devices, but also to very low losses due to air damping. As a result, the 2nd generation devices are very sensitive, which means that already at low driving speeds, sufficient output power for the TPMS application will be generated.
Piezoelectric approach
Layout, materials and process flow of the 1st generation of piezoelectric harvesters
Piezoelectric material has the property of generating a voltage along it when mechanically strained. It is well-known that microelectronic technology can be used to build tiny mechanical structures able to move and interact with integrated electronics. With these two premises, we have been working on the development of energy harvesters compatible with silicon technologies. The use of novel piezoelectric nanostructures and the way of easing their integration with silicon have been explored in this project. In our case, the configuration selected for the energy harvested is based on a cantilever structure, covered by the piezoelectric material, with a tip mass. However, in contrast to the electrostatic case, the work done in this project about piezoelectric technology has been more focused on discovering these new materials than in obtaining an operational device.
From the point of view of materials, we have invented a way to control the selective-area growth of ZnO planar nanostructures. They can be grown much faster than the typical nanowire, better reproducibility and high quality and coverage. An electrochemical method to activate gold seed layer has been also created to improve the reproducibility and uniformity of the growth of nanowires.
An in-depth characterization including, SEM, TEM, XRD, in-situ picoindentation and piezoresponse AFM have been carried out with excellent results. In addition, the following three hybrid devices were developed to gather an independent knowledge on the MEMS structure, the piezoelectric nanomaterial and polymer encapsulation and electronic integration:
AlN-based device mounted on an ad-hoc PCB:
The same MEMS technology and identical design have been used to fabricate a piezoelectric energy harvester of 25 mm2 based on an AlN thin-film. A generated voltage of 0.2V at a resonant frequency of 688 Hz was measured for an acceleration of 0.1G and a load resistor of 1MΩ.
Flexible generator based on ZnO NS embedded in polymer:
The piezoresponse of the whole structure comprised of metal-polymer-ZnO-AlN-metal has been measured by PFM (Piezoresponse Atomic Force Microscopy) obtaining an effective piezoelectric coefficient of 2.7 pm/V. Also, in order to demonstrate the capability of using ZnO NSs for energy harvesting, a flexible test structure comprised of a stack of metal-polymer-ZnO-AlN-metal was fabricated and characterized under periodic bending and a constant vibration.
cm-scale energy harvester based on PDVF and attached tip mass:
We have manufactured several devices based by integrating PVDF, polystyrene, silver ink, acrylic adhesive, and epoxy. The 1st generation prototype had a resonance frequency around 32 Hz, a maximum RMS open-circuit voltage of 17.5 V at an optimum load resistance of ~10 MΩ, and a generated power of ~30 µW for an input harmonic acceleration of 1 G. It can be translated to a power density of ~10 µW/cm 3. Thanks to an optimized design, the new prototype exhibits a resonance frequency of 50 Hz, a peak-to-peak voltage of 80 V with a load resistance of ~10 MΩ for an input harmonic acceleration of 2 G. It can be translated into a generated RMS power of ~80 µW (more than 4 times higher).
Layout, materials and process flow of the 2nd generation of piezoelectric harvesters
A batch of 8 wafers with piezoelectric energy harvesters has been just fabricated according to the improved 2nd generation device architecture and process flow. Several optimizations have been performed regarding the designs of the 1st generation devices:
- 90-degree corners have been filleted to avoid lines of high stress that could lead to premature fracture at resonance.
- Dependence between mass-beam lengths has been optimized to maximize power output.
- Several novel designs with multifrequency resonance or tri-axial motions have been added.
- A frame patterned by DRIE has been defined around each chip perimeter to allow the dicing of the wafer with tweezers.
In addition, several process versions have been run in parallel. Specifically, a simplified run has been used to create MEMS platforms with the same designs but without piezoelectric layer or top electrode. This allows performing the deposition of the ZnO nanostructures and the protective polymer by means of a hydrothermal growth followed by inkjet printing of SU8 and silver/gold inks.
Preliminary experiments show a good covering of the NSs, good adhesion of the SU8 to the wafer, and successfully metallization of the SU8 top surface with silver ink to create the second electrode.
In conclusion, several process versions have been run in parallel including a simplified run which will results in the creation of MEMS platforms that allows depositing the piezoelectric layer and the top electrode as post-processes by using hydrothermal growth followed by inkjet printing of SU8 and silver/gold inks. This is considered a highlight of the project since it may lead to a great simplification of the fabrication of such devices. These devices and their characterization will be finished after the project, but in the meantime several hybrid prototypes have been characterized: (1) AlN-based device mounted on an ad-hoc PCB with a power of 0.2 µW for 0.1 g of acceleration, (2) a flexible generator based on ZnO NS embedded in polymer, measured by PFM to obtain an effective piezoelectric coefficient of 2.7 pm/V and (3) an cm-scale energy harvester based on PDVF film and attached tip, with an RMS power of around 130 µW (and 76 Vpp) at 2 g for an optimum load impedance of 10 MΩ. The team responsible has secured the follow-up of these developments through a recently granted a new project (ENSO –Energy for Smart Objects of the ECSEL JU).
Thin film solid state batteries
LiMn2O4 based battery
LiMn2O4 (LMO) has been first considered to be used as an intercalation electrode for a high voltage cathode material. This material has been grown using RF-sputtering, pulsed laser deposition (PLD) and a solid state reaction (SSR) process. The material holds a theoretical capacity of around ~154 mAh/g and an outpum voltage of 3.5-4.5V. Thin layers of LMO have been characterised in detailed within the SiNERGY project. IMEC has prepared LMO films through RF-sputtering to be considered for full stack planar battery cell development and through electrochemical deposition of MnO2 and post-lithiation conversion through SSR which is a compatible process towards a 3D solid state battery cell assembly. IREC has fabricated LMO layers trough PLD.
Planar full-stack battery cells were fabricated. Battery stacks based on LMO cathode electrode, LiPON solid electrolyte and Lithium anode electrode have been characterized and tested. This thin film solid state battery stack shows 92% of the theoretical capacity. This battery stack delivers a potential of 4.1 V and can achieve a power of 0.24 mWh/cm2 at 0.1 C rate. The battery stack is encapsulated in a 2 x 3 cm glass. The encapsulated battery is taken out of the glovebox to ambient air and still an open circuit potential of 4.1 V can be measured.
IREC has explored a novel approach for the fabrication of a full battery stack exploiting the exceptional capabilities of the spinel LiMn2O4 optimized cathodes. This advance is presented here as an alternative full battery stack, which can be useful in some applications due to its extremely fast performance and simplicity of fabrication. The stack is formed by a LiMn2O4 cathode, aqueous liquid electrolytes (that do not have the safety drawbacks of organic electrolytes) and Zinc foil. The thickness of the battery based on its three components (cathode, separator and anode) is lower than 30 µm, considerably inferior to the 500 µm of the silicon substrate. A full cell comprising 1 µm LMO as cathode, a Zn foil with 1 µm of thickness as counter electrode and a Celgard separator with thickness of 25 µm soaked with 1 M Li2SO4: 20 mM Zn SO4 solution, was tested.
The capacity of this cell reaches a value of 50 µAcm-2 under a current rate of 0.7 C (the cell is cycled in less than 42 minutes). The cell maintains 70% of this capacity after an increment of the current rate of 43 times, (the cell is cycled in less than 2 minutes). The potential delivered by the battery is close to 1.9 volts because to the contribution of the LMO cathode and Zn anode electrodes.
Li4Ti5O12 based battery
Li4Ti5O12 (LTO) is a competitive candidate as an electrode material for Lithium ion batteries since it has a stable operating voltage vs lithium (1.55V) very small structural change (negligible volume expansion) and it can be easily obtained by several routes. IMEC has prepared LTO films through RF-sputtering to be considered for full stack planar battery cell development and post-lithiation conversion of TiO2 which is a compatible process towards a 3D solid state battery cell assembly, IREC has fabricated LTO layers trough pulse laser deposition.
Planar full-stack battery cells were fabricated. Battery stacks based on LTO cathode electrode, LiPON solid electrolyte and Lithium anode electrode have been characterized and tested. In order to increase the capacity of the battery, LTO thicker films have been used to develop a full battery stack. 500nm LTO films have been deposited by means of RF-sputtering. The electrochemical performance of this stack has been studied. Cyclic voltammetry shows the characteristic peaks for LTO and charge/discharge cycles show a flat plateau at 1.55V. This battery stack achieves full theoretical capacity at 1C. At 10 C rate (300 μAh/cm2) the battery stack reaches 50% of its capacity with a 99% coulombic efficiency. This battery stack delivers a potential of 1.5V and for the first battery stack delivered we could achieve a power of ~0.225 mWh/cm2 (500nm LTO film).
3D thin film battery proof of concept
For 3D geometries and Si compatible stacks several materials have been investigated in order to explore conformal depositions and post-lithiation of individual films towards a 3D solid state thin film battery. The 3D architectures contemplated are based on a hexagonally arranged array of Si pillars etched into the Si substrate with pillar diameter of 2 µm, an inter-pillar distance of 2 µm and a pillar length between 60 µm-100 µm.
Lithiation schemes have been established for electrode layers. Manganese Oxide, MnO2 (~3 V) has been used to do a post-lithiation step through a solid state reaction (SSR) to create LMO electrode layers (~4.2 V). The growth of the initial films is done through 3D compatible deposition techniques called Electrochemical deposition (ECD). Film deposition and post-deposition lithiation of individual thin films and half cells were evaluated in planar geometry. Moreover, MnO2 has been deposited conformally in 3D geometries with high aspect ratio and has proven to be a well suited material to work as a positive electrode material for the next generation thin film batteries. This LMO electrode has shown promising results to be used in 3D micro-batteries. Recent results have shown that MnO2 can be easily platted on 3D structures showing good conformal deposition and electrochemical behavior. ECD MnO2 film LMO grown on 3D pillar structures have been successfully converted into LMO by post-lithiation. The 3D electrode arrangement shows an enhancement of a factor of 20 compared to a planar LMO thin film of the same thickness (~350 nm).
The preparation of conformal electrolyte layers through a solid state reaction (SSR) have shown to be challenging. LiTaO3, Li2NiGe3O8 and Li4Al4-3xSiO4 electrolytes have failed to provide the ionic conductivity and morphology needed for battery stack development and for 3D structuring. For planar thin film batteries SiNERGY has considered the solid electrolyte Lithium Phosphorous Oxynitride (LiPON) as backup material. This material is at the moment not compatible for 3D thin film battery technology. Hence, it is not trivial to think of an adequate solid state electrolyte which shows conformality and high ionic conductivity. At this point, IMEC has taken the knowledge they have in battery technology and specially in solid composite electrolyte (SCE) components and has implemented this type of materials within the SiNERGY project as an alternative. The SCE is based on a matrix which conducts Li-ions very easily and can be used as a filler for the 3D pillar arrays. This approach has led to a 3D thin film proof of concept device: LMO/SCE/Li (~4.2 V).
Feasibility integration in application scenarios
Fully autonomous tire pressure monitoring system (TPMS) demonstrator
Tire pressure monitoring systems (TPMS) are mandatory in USA and Europe in new cars since 2008 and 2012 respectively. The main parameters to sense are pressure and temperature of the air inside a tire. The measurement frequency depends on how fast is necessary to detect a possible puncture; usually a 5 to 10 second measurement rate is acceptable. For the autonomy of this TPMS demonstrator vibrations and shocks generated at the inner-liner of the tire will be used. There are two reasons to transfer from the standard TPMS on the valve to the inner-liner of the tire: much higher vibration levels and possible added functionality beyond pressure, resulting in a so-called ‘intelligent tire’. Small, cheap and robust vibration energy harvesters made with silicon processing are used to obtain autonomy without using batteries.
The electrostatic vibration energy harvester developed by Imec-NL was combined with the ultra-low power TPMS module of STE. The module did not contain a battery and only the power generated by the harvester was used. The energy harvester improvements obtained in SiNERGY resulted in higher power generation at lower excitations and much better reliability. Especially, the reliability is known to be the challenge of using brittle silicon in applications with high impact shocks. Shocks in the tire at normal driving conditions can already amount up to 150 G for 60 km/h. Much higher accelerations can occur during driving on e.g. bad roads and TPMS integrated in the tire should withstand acceleration exceeding 2000 G. The silicon based harvester was improved by optimizing the springs and introducing efficient damping by introducing flexible silicon bumpers. Such 2nd generation devices with reliability improvements do not break up to 2000 G.
The system was tested in the lab and was fully operational at very low vibration levels. At those low vibration level (~10-4 g2/Hz) the pressure was measured and sent every 10 seconds. The power needed was only ~4µW!! It scales linearly with noise level and at 2 times higher level, the pressure measurement was sent every 5 seconds. This result was possible due to development of STE’s ultra-low power TPMS module and the improvements on the energy harvester.
Thermal electric generator (TEG) demonstrator
The temperature measurement in Foodservice Industry is extremely important for two reasons:
i. Food safety. Time and temperature are the two most important factors to control and monitor in the prevention of food borne illnesses.
ii. Quality and performances. Temperature is a parameter equally critical to obtain the desired quality of the cooking. For perfectly fried foods, it is critical to keep the oil at the correct temperature.
Industrial fryers are gas-powered, unplugged industrial appliances. EC regulations require oil quality to be monitored using a log of oil temperature as a function of time. Thermal harvester may then supply the power needed to monitor oil temperature and to transmit data through a wireless connection to a remote data logging system without the burden of wiring the fryer to the electric net. The industrial fryer was used as a waste heat resource for a commercial in order to test the feasibility of the system.
The signal is transmitted by an ultra-low power 434 MHz RF module with pulse-based transmission, provided with a microcontroller from MSP430 family. A J-type thermocouple was used as a temperature monitor connected directly with the microcontroller. Integration tests were performed to anticipate assembly issue that might show up at the module level in the demo application using a commercial off-the-shelf TEG by Marlow Inc. using Bi2Te3 thermoelectrics with a nominal power output 5 times larger than the SiNERGY top-down thermal harvester. They led to identify the optimal hot point on the fryer metallic framework to be used to collect heat, to set a proper module assembly, and to define a suitable heat dissipation strategy. Results showed that the assembly allowed the RF transmitter to be powered and to transmit data with a frequency larger than 0.5 Hz with less than 5 seconds of initial latency without any need for a battery to accumulate power. This implies that the SiNERGY thermal harvester may provide a sufficient power output out of a surface of about 60 cm2, largely compatible with the available hot wall size. Tests also provided clear evidence of the importance of an efficient heat dissipater to prevent temperature equilibration across the TEG after a few minutes of operation.
Piezoelectric energy harvester (PEH) demonstrator
Finally, a third integration exercise has been performed to cover one of the use cases projected at the beginning of this project. This use case focused on predictive maintenance, which is a novel concept on industrial maintenance based on the idea of predicting a machine failure before it occurs by means of the monitoring of several parameters, such as vibrations or temperature, to find precise patterns that are faithfully related to the imminent failure. Therefore, the environments of application are industries, factories or vehicles, where ambient vibrations are present. Therefore, we decided to use vibration-driven piezoelectric energy harvesters to cover this application.
The technology used to fabricate this demonstrator is based on piezoelectric polymer, instead of a silicon based devices, due to the higher degree of maturity and higher power generation. We have used a kit EZ430 (Texas Instruments), which contains a full-equipped sensor node with wireless connection and different sensors (temperature, pressure and 3-axes accelerometer). Several power management circuitries have been utilized to rectify and manage the power scavenged. The choice of using one or other depends on the application. Basically, the current generated has to be rectified, the charge accumulated and the subsequent voltage adapted to the requirements of the node of application.
We have configured a characterization setup that allows applying controlled vibrations to the energy harvesters. The energy harvester has been designed to resonate at 50 Hz, obtaining a peak-to-peak voltage of 80 V for a load resistance of ~10 MΩ, and an input sinusoidal acceleration of 2G. Therefore, this means a generated RMS power of ~80 µW. After using a power management circuit, an effective power of 22 µW can be generated, corresponding to an efficiency of ~20%. It allows the operation of the EZ430, which requires less than 100 µW for a normal operation of waking-up, sensing, transmission and going to sleep mode again. For instance, for the case of the rotor of a helicopter or the train wheel set, where a vibration of around 20-60 Hz and 1-2G is present, 1 min of charge will allow 1 second of operation, which should be enough to allow continuous unassisted operation of the node.
Potential Impact:
SiNERGY focuses on silicon and silicon friendly materials and technologies to explore energy harvesting and storage concepts for powering microsensors nodes. SiNERGY selects a series of relevant examples of power microgeneration and storage (thermoelectric generators, mechanical harvesters and microstructured batteries) with the aim of pushing them further into their development and performance maturity. With that goal in mind, emphasis is placed on thin films and nanostructured materials and their integration route into a technology able to bring the eventual solutions closer to an exploitable phase. For this reason, we consider silicon technology compatible materials as our starting point. Silicon technologies provide an enabling path to miniaturization, 3D architectures (improved energy densities), mass production with economy of scale, and the ability of power intelligence integration. Harvesting energy, tapping into environmentally available sources such as heat and vibrations, may be a good solution in man-made scenarios applications. 10-100 μW/cm2 seems appropriate for many such applications. Coupling those harvester devices to secondary batteries to buffer enough energy to account for the power demand peaks required by the communication unit of wireless nodes would be an enabling energy autonomy solution.
Energy autonomy keeps being one of the most desired enabling functionalities in the context of off-grid applications, such as wireless sensor networks (Internet of Things, Trillion Sensors). Micro and nanotechnologies have already made possible the fabrication of small, low cost and good performance sensors that are called to be protagonists of continuous monitoring scenarios and distributed intelligence paradigms. Such technologies are the prime candidate for building microenergy solutions of similar robustness able to power such sensors during their whole lifetime.
Even though SiNERGY focuses in the materials and technologies leading to harvesters and storage devices, attention was paid to real applications scenario. As a consequence, while the focus is placed on the devices themselves, system level integration issues have been considered as well, to keep in mind application-wise all the elements required by an eventual autonomous working sensor node, and to consider which of them may have an impact in some of our device architectural choices.
SiNERGY results and exploitation scenarios
During its lifetime, SiNERGY project produced several results in terms of advancement of knowledge (14 items) / preliminary foreseen commercial exploitation (four items) in the field of microdevices for energy harvesting and storage (See the PUDF section for more details). Also four patents are at different stages of submission, namely:
(1) System and device for collecting piezoelectric energy // submitted by CSIC // WO2016ES70381
(2) Method for fabricating Solid-State Thin Film Batteries // submitted by imec // EP16168461 – US15146714
(3) Bioelectonics device based on piezoelectric and magnetostrictive materials for cellular interaction and neural stimulation // in process, by CSIC // EP16411241 (preliminary number)
(4) Method for forming Lithium Manganese Oxide Layers // in process, by IMEC
These results have been gathered in five major findings), or Key Exploitable Results (KERs), in order to better describe the potentiality behind their exploitation, and to explore the impact that such new material solutions for low-cost, miniaturized and environmentally friendly applications can have on societal and economic issues. It is worthwhile noting that the combination of any of those KERs configures, actually, all the possible SiNERGY microenergy solutions:
KER1 - Microenergy solution based on a thermoharvester (bottom-up design)
KER2 - Microenergy solution based on a thermoharvester (top-down design)
KER 3 - Microenergy solution based on an electrostatic mechanical harvester
KER4 - Microenergy solution based on a piezoelectric mechanical harvester
KER5 - Thin film micro-battery
Short SiNERGY KERs’ descriptions are reported below, with a sketch on their innovativeness and unique selling proposition.
A collaborative risk analysis with focus on key risky factors has been performed. Risk matrices are reported for each KER, describing, for each different source of risk, the success of the potential/provided intervention and the related risk grade.
A self-explicative synoptic table, which condenses in a glance the expectations and the nature of the activities foreseen for the project results by each of the consortium partners, is also presented within each KER’s paragraph.
In relation to the role of the companies of the consortium, it must be said:
- Manufacturing energy harvesters is not the core business of Electrolux, but it is firmly convinced that Autonomous Energy Efficient wireless sensors powered by low-cost energy harvesters may find a place in Smart Appliances produced by Electrolux, and in predictive maintenance schemes in Electrolux production facilities.
- STE is deeply interested in energy harvesting as a complement to its micro.sp communication technology for wireless sensors networks. However, manufacturing energy harvesters is not the core business of STE, and only if such harvesters were commercially available at high numbers/low cost STE may consider market operations in the Autonomous Energy Efficient Wireless Sensors field as part of the value chain.
KER1 - Microenergy solution based on a thermoharvester (bottom-up design): this is a solution for energetic autonomy based on a microthermoharvester (with bottom-up silicon nanowires as thermoelectric material) with appropriate power management. It does not need primary batteries or wired power. The innovativeness stands in the production of harvesters using silicon nanowires as thermoelectric material, built following a monolithic approach that uses high-density integration of nanowires by means of bottom-up techniques. Unique selling proposition: this harvester is a combination of microdevices built with materials and processes compatible with silicon technologies (scalable technologies, with size/cost reduction) following a technological path of low complexity. It requires the employment of low-cost, geo-abundant, environmental-sustainable, and non-poisonous raw materials. It should be moreover considered that, as will be showed in the section “Social and economic implications”, that energy extracted from waste heat sources is contained in the device’s application scenario.
KER1 Expectations Table
Manufacturing, Realisation: CSIC, IREC
Assembly: ELUX
Research: CSIC, CERR, ELUX, IREC, STE, UNIMIB
Consultancy, Training: CERR, STE
Utilisation in other business: CERR, STE
Saling, distribution: --
Services: --
KER2 - Microenergy solution based on a thermoharvester (top-down design): this is solution for energy autonomy based on a combination of microthermoharvesters (with top-down silicon nanowires as thermoelectric material) with appropriate power management. It does not need primary batteries or wired power. The innovativeness stands in the production of harvesters using silicon nanowires as thermoelectric material, built following a monolithic approach using medium density integration of nanowires by means of top-down techniques. Unique selling proposition: the technology is a combination of microdevices built with materials and processes compatible with silicon technologies (scalable technologies, with size/cost reduction, and with abundant material). It uses inexpensive, geo-abundant raw materials, indeed. As for the previous KER, this technology may use energy extracted from waste heat sources too.
KER2 Expectations Table
Manufacturing, Realisation: CNR
Assembly: ELUX
Research: ELUX, STE
Consultancy, Training: CERR, STE
Utilisation in other business: CERR, STE
Saling, distribution: --
Services: --
KER 3 - Microenergy solution based on an electrostatic mechanical harvester: this solution is an energy autonomy solution based on a combination of electrostatic MEMs-based mechanical harvesters. As for the previous technologies, it does not require primary batteries or wired power. The innovativeness of the solution stands in the small size, the monolithic approach, the improved reliability and in the improved moisture resistance of the device. Unique selling proposition: this is a combination of microdevices built with materials and processes compatible with silicon technologies (abundant material, scalable technologies, with size/cost reduction). The application scenario considers, additionally, the use of energy extracted from vibrational and/or shock sources.
KER3 Expectations Table
Manufacturing, Realisation: --
Assembly: --
Research: imec-NL, STE
Consultancy, Training: CERR, imec-NL, STE
Utilisation in other business: CERR, STE
Saling, distribution: --
Services: --
KER4 - Microenergy solution based on a piezoelectric mechanical harvester: this microenergy solution is based on the employment of different piezoelectric energy harvesting technologies. Its innovativeness consists of a monolithic integration of an energy harvester, rectifier diodes and an intermediate storage capacitor. It uses ZnO nanostructures and polymer layer as piezoelectric layer, with a remarkable robustness increase. Unique selling point: the presented solution is a monolithic solution, with a smaller size, a higher integration and a cost reduction. Nanostructures are employed instead of thin-film, conferring higher robustness, and opening wider application scenarios. In-situ rectification/storage means the possibility of building arrays, which results in higher power, broader vibration spectrum and higher efficiency. Use of flexible substrates, moreover, implicates more robustness, lower resonance frequency and low cost.
KER4 Expectations Table
Manufacturing, Realisation: CSIC
Assembly: CSIC
Research: CSIC
Consultancy, Training: CERR,
Utilisation in other business: CERR
Saling, distribution: --
Services: --
KER5 - Thin film micro-battery as a stand-alone product: this battery is a fully functional all-solid state thin film battery, that could provide the power needed for microdevices such as energy harvesting solutions. The employed materials are produced through scalable technologies for size/cost reduction, following a technological path towards the complexity of 3D thin film batteries, aimed to increase cell capacity for the same area footprint. The innovativeness is that these all-solid state microbatteries are based on an all-spinel configuration, providing high capacity and power. In addition, 3D thin film microbatteries are suitable for high-capacity/power demanding applications. Unique selling proposition: this technology is a unique concept of Si-compatible, 3D all-solid state thin film battery.
KER5 Expectations Table
Manufacturing, Realisation: imec
Assembly: imec
Research: IREC, imec
Consultancy, Training: CERR, imec
Utilisation in other business: CERR, imec
Saling, distribution: --
Services: IREC, imec
Social and economic implications of the SiNERGY’s results
To better understand the scenery in which SiNERGY innovation is taking place, and the prospects of impact in social and economic terms that its results can generate, a brief analysis of the impact of some technologies and devices and that can benefit of these results is thereby presented. In details, a short overview on EU IoT strategies and impact is presented, followed by a focus on the microelectromechanical systems (MEMS) and the envisaged socio-economic impact of two MEMS devices that can specifically take profit of SiNERGY research outcomes and enter more effectively in our everyday life.
As a premise, we should consider that what we call socio-economic impact is usually driven by business, and is a major predictor of business success. Companies affect people’s assets, opportunities, capabilities, and standards of living in many different ways. Thus companies are on their side conditioned by their customer’s approval. As a result, companies are increasingly interested in measuring the socio-economic impact of their products, that is, as in our case, in the introduction of novel technologies on the market.
IoT landscape in EU
The EU2020 strategy for growth, with target objectives, priorities and initiatives for a smart, sustainable and inclusive growth, has been clearly defined. Within this strategy, ICT plays a strong role.
The “Internet of Things” concept, indeed, intended as the ever-growing network of physical objects that communicate via IP between them and with other Internet-enabled devices and systems, is fully aligned with this vision, and is expected to be an essential cornerstone to this industrial revolution.
Economic impact: the “smart growth” driving force in the EU vision relies on the development of a strong knowledge economy, and the IoT development in Europe is expected to support this vision intensely. In this sense, the research through EU is already at the forefront of the development of many of the necessary components of an internet of things. The market expectations for the IoT in the next years are very high, and are strictly related to the society needs and expectations. This market, and the related predictions, is, by the way, very complex, being driven by a multifaceted ecosystem of different actors that play specific roles: research organization, as key provider of technologies; existing Industrials as provider of supporting infrastructures for the ecosystem; data providers; SMEs and Start-ups for production of end user applications; regulation authorities.
Societal and environmental impact: EU is fronting inequalities between different regions/states, as well as demographic (ageing population) and societal challenges (unemployment is a critical issue in certain areas). In addition to supporting a “smarter” and more sustainable society, the Internet of Things vision can also have a decisive impact on the inclusiveness of society by supporting not only a higher quality of life but also reducing inequities. This impact is more evident on health, security and, of course, economic issues. Environmental Impact is also key to EU 2020 agenda. In this direction, there is a strong expectation from the society on the future role of IoT to address sustainability issues, and in particular sustainable food, resources, energies, industries and services, transports.
Microelectromechanical Systems (MEMS) in IoT
Sensors and actuators are critical devices for transferring information between the physical and digital worlds. While early sensors were large, bulky, and prone to failure, advances in miniaturization have led to micro-scale devices that can be combined on a single chip. These MEMS are already revolutionizing medical care, automotive and industrial diagnostics, and are poised to lead to rapid advances in haptic control, as accelerometers and gyroscopes are placed in every electronic device a person carries. As smartphones replace entire laboratories of equipment, the $12 billion MEMS market is experiencing annual growth rates of more than 20%.
Over the last decade there has been a growing emphasis on adding embedded intelligence to the world around us in order to make it smarter. This vision of smart encompasses cities, transport, energy, health, homes, and public buildings, among other areas. The goal of smarter environments and activities is driven by the complex mixture of challenges outlined in this chapter. We increasingly need creative solutions that can do more with less to meet these growing challenges. Innovation should be about bringing a great idea to market: 60% of the world population will live in cities by 2020, creating enormous challenges in delivering sustainable living environments for those city dwellers.
Sensors are playing and will continue to play a key role in enabling innovative solutions. Smart technologies—such as smart sensors, data acquisition systems, ubiquitous data connectivity, and big data analytics—provide key technology building blocks. Integrated appropriately, they provide efficiencies, scalability, and cost reduction. They also act as an innovation platform for long-term solutions to enable meaningful citizen engagement or “stickiness.” The potential of these systems will continue to evolve, particularly as the trajectory and merging of technologies increases.
One of the main challenges for wireless sensor networks is how to power these sensor nodes. Use of wired power limits the viable locations (and ultimately numbers) of sensor nodes and may preclude gathering essential information. Batteries, on the other hand, need eventual replacement. This is an expensive (and, in some cases, impractical) proposition for networks with large numbers of nodes, some or all of which may be dif cult to access. Moreover, batteries are constrained to a limited temperature range.
SiNERGY objectives foresee to overcome limits and support low-power sensor nodes targeting 2 of the products that are recognized among the most challenging in the Internet of Things:
1. Tire Pressure Monitoring System.
2. Autonomous device in home and industrial appliances.
The aim of the Consortium is to provide MEMS energy harvesters that convert environment vibration or heat into electricity. Current MEMS technology is not capable to create and deliver enough energy to power up sensors. Energy Harvesting in Tires is considered one domain in the area of the disruptive technologies that is widely considered as the most challenging in the Internet of Things universe of advances as it requires breakthrough in mechanical engineer, RF design, energy efficiency, robustness at high stress up to 3000g, resistance to automotive temperature that range from -40 +125°C. It also requires breakthrough and innovation in wireless communication such as ultra-low energy consumption, high power output, high rate of RF link margin budget, high performances in RF propagation and resiliancy to effect such as Doppler, multipath radiowaves propagation and other particular tasks. Sensors in tires are by far considered the first example of Internet of Things that is already commercially available (due to regulatory frames in US and EU) and sold in volume.
Generally, breakthrough technology classification, as in standard off the shelf technology, complies to following criteria:
1. Technologies must have progressed beyond lab-scale validation and have Signs of Economic Success. On the other hand, such technologies will have already shown signs of successful commercialization and are beginning to enter the marketplace: Even the most breathtaking innovations have severely limited utility if they remain conned to the laboratory due to high costs or missing infrastructure.
2. Interdisciplinary Impact: disruptive technologies, such as the Internet of Things and Energy efficient wireless and autonomous sensors, impact multiple industries simultaneously, becoming global phenomena. They have the potential to transform several industries simultaneously and are not limited in scope to a particular domain such as autonomous wireless sensors in tires or in industrial appliances.
3. Near term Consequences. In few decades our world will barely resemble the world of today. Yet, it is almost impossible to predict exactly how that world will be different: they must be on the cusp of major breakthroughs and expected to have significant impacts in the next decade.
4. Revolutionary Potential. They must be radically revolutionary and likely to disrupt, rather than extend existing industries. Although these technologies build on existing developments, they are likely to trigger significant changes to business models and practices as they are implemented.
Cooking vessels socio-economic impact
Domestic and professional appliances are equipment that uses a lot of energy but, in some cases, a significant part is lost. A typical example is a gas burner that, when used to heat a pot, has an efficiency of 60%. That means that 40% of the energy is wasted (most of it in exhausted gases). But there are several other examples of wasted energy: in boilers, pipes for hot water or steam transport, infrared heaters, heat exchangers and others.
With the ever increasing attention to the environmental sustainability and to the need of doing things better and better, the opportunity of using waste is becoming a must.
In SiNERGY Project it has considered a gas powered fryer, where part of the heat dispersed in the exhausted gases is converted into electricity to supply an electronic board. It is well known that gas-powered appliances, like the fryer, have no electrical energy on board and that is a great limitation in terms of control and monitoring. In fact, in these cases, the process control (oil temperature), is done thorugh an electro-mechanical component (thermostat based on fluid-expansion) that, for its nature, is not so accurate and cannot be even monitored from kitchen control systems.
A precise control of oil temperature is important because it affects characteristics of food (both for sensorial aspects than for health). Frying at a too low temperature make final food with too fat. Frying at too high temperature make it too dried and singed. This last fact is even worse because of acrylamide. This chemical doesn’t appear to be in raw foods themselves. It’s formed when certain starchy foods are cooked at high temperatures for long periods of time.
The temperature measurement in Foodservice Industry is extremely important also for other reasons:
Food safety
Time and temperature are the two most important factors to control and monitor in the prevention of food borne illnesses.
Infectious diseases spread through food or beverages are a common, distressing, and sometimes life-threatening problem for millions of people around the world.
After a number of food crisis, the EU marked a shift to a more pro-active food policy and a new legislation. The HACCP (Hazard Analysis and Critical Control Points) system represents the key element for an early warning system at the production site and enables manufacturers to take preventive measures based on real data and hazard analysis. HACCP is nowadays a globally used safety philosophy to ensure the safety of foodstuffs. The monitoring and control of food temperature is a cornerstone in the management of HACCP, and no one can give up.
Quality and performances
Temperature is a parameter equally critical to obtain the desired quality of the cooking, not only for fried foods. If the importance of food temperature measurement cannot be questioned, the usefulness of having it wirelessly is equally well known. Wireless food-probes are very handy, wiring of the equipment is simplified, and connectivity with central control unit is also simplified.
The combination between «energy harvesting» and «wireless communication» is then of special interest of gas-powered appliances that represents an important business in all South Europe Market (because of the cost of electrical energy). In these cases, to have an “electronic like control” without having “electrical/electronic appliances” is a competitive advantage (no electrical plug, no electrical certification).
This is becoming particularly relevant now that, «Internet of Things» model is entering more and more in everyday life, with a growing number of products that must be connectable to their ecosystems. The most important recent exhibitions in the world, like IFA in Berlin and CES in Las Vegas, has clearly confirmed this trend.
New Consumers, and digital natives are among these, expect to have almost everything connected to their smartphones. There is a growing need to monitor everything from everywhere. Doing that for pure mechanical products is impossible and that creates a sort of discomfort.
Digitalization allows improving even those processes that have been up not so close. Cooking is among these and there is an increasing attention to it.
From the industrial point of view, the possibility of using a thermal harvester to power an electronic board is not a minor point. There is no need to have plugs, cables, power supply units nor batteries that could be the alternative solution. It is not necessary to certify the equipment to LVD (Low Voltage Directive). Also it is an advantage from the environmental point of view since useful work can be done with the energy already available.
Improved tire efficiency socio-economic impact
Use of vehicles in general showed that the working condition of tires, besides subjective driver behaviour, should be monitored by controlling the air pressure inside the tire: being the sole part of the vehicle that is in constant contact with the ground, the “tire contact patch area” it is important on constantly monitor its condition as a function of inflation rate. The correct positioning of the “tire contact patch area” significantly affects vehicle’s security, and contributes to Rolling Resistance rate of vehicle that can increase fuel consumption due to higher exhaust emissions. In addition, defective tires reduce vehicle performance, reduce braking and acceleration efficiency and reduce the efficiency of management and driving comfort.
It is therefore considered as a mandatory task to put considerable attention directed towards the control and management of the correctness of the tire condition by monitoring tire pressure and inflation as reported in the tire placard. An important element for controlling the tire pressure levels is the so called TPMS (Tire Pressure Monitoring Systems) devices that some countries ruled out as a mandate to install such system in vehicles with aim to improve safety and reduce pollution.
As a consequence of the directive of such system in the territory of the USA (NHTSA FMVSS138), in 2007 Bridgestone conducted extensive research in 19 EU countries. The results showed that as many as 38% cars used tires inappropriately inflated, contributing to increase danger in road traffic and CO2 emission because of a higher rolling resistance and consequent increase of friction and rate of dynamic.
Similar studies conducted in Europe clarified that approximately 90% of European motorists drive with at least one tyre underinflated and 12% drive cars with tyres in danger of failure. Tyre underinflation poses significant concerns on (i) safety in vehicles, since 9% of fatal accidents on motorways are related to tyre failures because of tire wear, and (ii) environment, as it contributes to the waste of billions of litres of fuel and around 10 MT excess in CO2 emissions. The recently adopted EU’s General Safety Regulation prescribes that ‘accurate’ systems should be fitted to new cars as of 2012 to increase safety and reduce CO2 emissions. The regulatory body UN-ECE, similarly to US mandate following to NHTSA FMVSS138 prescription, has recently required the mandatory use of TPMS in vehicles on the European territory.
Thus the widespread adoption of tire efficiency programs over the next decade will reduce vehicle fuel consumption by approximately 3%, and reduce global well-to-wheels greenhouse gas emissions by 100 million metric tons per year in 2020. This improvement would avoid the emission of more than 45,000 metric tons per year of nitrogen oxides and 10,000 metric tons per year of fine particulates from upstream fuel production and refining.
SiNERGY Dissemination activities
SiNERGY’s Consortium partners have been involved in wide dissemination activities, which mainly proceeded via website, conferences, international fairs, workshops and public speeches. A well-defined and structured set of dissemination activities has been carried out to foster awareness of SiNERGY main results in the society, scientific community and industry, thus facilitating the exploitation of Micro and Nano-powered sensors and smart system solutions in a wide range of application sectors.
Three SiNERGY main events have been organized, in conjunction with other relevant European initiatives to share and exchange ideas. Furthermore, as research turns in results, the relevant activity not subjected to IPR restriction has been made public available. All the activities have been recorded on the PUDF – Section A.
Attention has also been given to keep updated the SiNERGY website in its public area with news and other relevant information, while the private area has been enriched by reserved documents.
Scientific publications and generic information for common people, calendar to relevant international events, and general advertising have also been made publically available. Relevant scientific and technical results have been published in international journals mainly referring to sensors, electronics, microenergy, nanomaterials and MEMS technology, in such a way reaching all the main target groups identified in the dissemination and exploitation strategy. Similarly, a project presentation, project poster, project leaflet, two newsletters and two videos (a 2” short one - https://www.youtube.com/watch?v=lOwmP6n4G1s and a 11” extended one - https://www.youtube.com/watch?v=dADrj1W3Eis) have been produced.
The analysis of PUDF-A, devoted to track dissemination activities, shows the following main results with a very good overlap with the target groups identified in deliverables D6.2:
✓ 90 dissemination events in total (among which 48 conferences & workshops, 16 presentations/posters/other and several videoclips)
✓ > 7200 people involved in the events;
✓ 8 press articles published
✓ Close to 30 peer reviewed scientific publications / book chapters
All partners were involved in the dissemination according to their roles and results achieved, contributing to the presentations delivered by the project coordinator and WP leaders/deputies thus actively participating in UE working groups, EU sponsored events and Technological Platforms for project visibility.
The SiNERGY website has been periodically monitored by Google Analytics to gain further insight in terms of communication efficiency and functionality, further optimized in Search Engine Optimization context. To date, the analysis discloses worldwide connections with constantly rising shares from new connections as result of dissemination events carried out by SiNERGY partners and the Search Engine Optimization activities.
The three main dissemination events mentioned before are:
• SiNERGY 1st workshop, as a part of the LET’S 2014 international conference held under the Italian presidency of the EU, which dealt with the role of Key Enabling Technologies – Bologna, 29th Sep - 1st Oct 2016
• SiNERGY 2nd Workshop, inside the Energy Harvesting Systems – “FlexTEG” - June 25-26, 2015 @ Fraunhofer IWS Dresden
• E-MRS SIMPOSIUM W [Materials and systems for micro-energy harvesting and storage]- held in the general frame of the E-MRS Spring meeting (2-6 May 2016) in Lille (France)
They were organized according to the spirit of the planned activities in the DoW. For the later, it was decided that opting for an open symposium rather than a closed workshop was worth trying from the point of view of a broader dissemination of SiNERGY goals and general micro-energy issues and that was the case.
So far it is worth mentioning that, in addition to SiNERGY (GA nº604169), the symposium counted with the help and support of other EU funded storage and harvesting projects such as NanoCaTe (GA nº604647), MATFLEXEND (GA nº604093) and MANpower (GA nº604360), which provided both members for the scientific committee and some proposals for invited speakers. This was also the case for the second SiNERGY workshop, which was sponsored by the NanoCaTe project.
To their own extent, the three SiNERGY events have offered a wide and international platform for discussion on energy harvesting materials, storage materials, integrated systems for energy harvesting and storage, applications and business scenario.
As an aftermath of these four European projects joining their forces, a common presentation of their works in the field of energy harvesting and storage was accepted in the Industrial Technologies event held June 22-24 in Amsterdam under the Dutch presidency of the EU. On such occasion, SiNERGY had the opportunity of advocating for the microenergy topic presenting the complementary approached of the four projects. This role also extended to the participation in a concurrent meeting of the Advanced Materials and Nanotechnologies for Energy Applications Cluster, which portrays an initial orientation biased towards macroenergy applications. In this respect, SiNERGY stressed the intrinsic and practical interests of microenergy regarding both materials and nanotechnologies and pointed to the fact that in our case nanotechnologies are not only a mean to improve materials as mostly done by macroenergy approaches but also to fabricate the microenergy devices themselves.
List of Websites:
sinergy-project.eu
Energy autonomy keeps being one of the most desired enabling functionalities in the context of off-grid applications, such as continuous monitoring scenarios and distributed intelligence paradigms (Internet of Things, Trillion Sensors). SiNERGY has focused on silicon and silicon friendly materials and technologies to explore energy harvesting and storage concepts for powering microsensors nodes. Harvesting energy, tapping into environmentally available sources such as heat and vibrations, may be a good powering solution in man-made scenarios applications. 10-100μW/cm2 power densities seem appropriate for many such applications. Coupling those harvester devices to secondary batteries to buffer enough energy to account for the power demand peaks required by wireless nodes would be an enabling energy autonomy solution.
SiNERGY has selected relevant examples of power microgeneration and storage (thermoelectric generators, mechanical harvesters and microstructured batteries) pushing them further into their performance and development maturity. Emphasis has been placed on thin films and nanostructured materials and their integration into mechanically and thermally optimized microstructures. For bringing the eventual solutions closer to an exploitable phase, silicon technology compatible materials have been considered. Silicon micro and nanotechnologies provide an enabling path to miniaturization, 3D architectures (improved energy densities), mass production with economy of scale, and the possibility of easy integration with other microchip based devices (sensors & actuators, power management circuits, communication units...)
Silicon friendly materials and device solutions for thermoelectric harvesting. Thermoelectric microharvesters able to convert heat flows into small, yet high added value, amounts of electric power have been pursued. The activity has focused in successfully integrating silicon nanowires as low thermal conductivity material into devices with optimized thermal and electric design. Both, bottom-up and top-down approaches for nano-objects integration have been explored.
Silicon friendly materials and device solutions for mechanical energy harvesting. Electrostatic and piezoelectric harvesters have been explored to convert small vibrations into a useful power. In the first case, an optimized silicon based electret material has been integrated in a robust laterally moving microstructure. In the second, the integration in vertically moving microcantilevers of a piezoelectric composite based on ZnO nano-objects has been attempted, and a hybrid fabrication approach combining silicon and printing technology has been shown promising.
Silicon friendly materials and device solutions for solid-state microbatteries. Material and interface optimization (from a fast charge/discharge perspective) has led to the fabrication of a functional thin-film planar microbattery for on-package energy storage. Translation of this knowledge into 3D microbatteries, fully compatible with Si technology, for increased capacity and power has been attempted. Failure to identify a good solid electrolyte has prevented full success, but a hybrid 3D battery has been assembled.
Integration feasibility. Even though SiNERGY focuses in materials and technologies, attention has been paid to real applications. As a consequence, system integration issues have been tackled at different levels for the above microenergy devices. A gas fryer scenario has been explored for the deployment of thermal harvesters, piezoelectric devices have shown appropriate for powering remote nodes at useful duty cycles (e.g. for preventive maintenance), and the electrostatic harvester has been shown functional in a Tire Pressure Monitoring application.
Project Context and Objectives:
SiNERGY in a nutshell
The project addresses the development of energy harvesting and storage devices suitable for solving energy autonomy issues of unwired powered devices working in low-power and/or pulsed regimes that will be required in continuous monitoring scenarios. The combination of an energy harvester with a small-sized rechargeable battery is the best universal approach to enable energy autonomy in those applications.
The microenergy elements of interest for SiNERGY are then harvesters and solid-state batteries. In the case of harvesting, thermoelectric and mechanical harvesters have been considered given that temperature differences and vibrations are the most common environmental energy sources in manmade scenarios. The focus of the proposal is placed on the microdomain to obtain small size devices with high energy density features, and on the silicon technology friendliness of materials (and approaches) to assure the eventual manufacturability, integration and cost effectiveness of the related devices/solutions.
When resorting to silicon technologies, the material issue cannot be dissociated from the architectural issue, which unavoidably brings the focus closer to the device level. This is an added value because the development and exploitation of the devices is moved one step further into maturity. For this reason, not only different low dimensional material options (crystalline and polycrystalline Si nanowires, Si-Ge nanowires, ZnO nanoobjects, and oxide, nitride and metal thin-films) are considered, but also different technological fabrication approaches (bottom-up or top-down approaches), and device architectural alternatives (micromachined thermally isolated platforms, micromachined in-plane or out-of-plane movable platforms).
The high volume, cost-effective and sustainable fabrication enabled by micro and nanotechnologies will support the advent of energy autonomy solutions required by the eventual success of numerous applications. Three of these applications have considered as a frame of reference for our developments: tire pressure monitoring systems, smart cooking appliances (as an example of machine condition monitoring), and generic preventive maintenance. As a test case, each presents a different harvesting scenario: vibration in the first, hot surfaces in the second, both in the third (always it will be used for vibrations in our case) and a different motivation for going into the microdomain (physical space constraints in the first and the second and multiplication of nodes in the third case).
SiNERGY context (1): microenergy vs macroenergy
We are talking here of microenergy, tiny bits of energy and a few microwatts of power, not of the 10^16 TW that yearly are produced worldwide. Society of today needs abundant energy to power our cars, factories and homes, but society of tomorrow will also need abundantly distributed energy to power the billions of sensors that will be deployed in the Internet of Things to come.
We are not referring either to ‘microgrids’ (which is an abuse of language for designing locally redistributed macro energy sources). We use the term micro to really refer to miniaturized cm-size devices. Silicon technologies are the techniques of choice in SiNERGY. Other large volume, cost effective technologies exists that are also miniaturization-prone to some extent, such as lamination or printing technologies. They even excel over Si Technologies when producing cheap large area devices or flexible devices, but Silicon technologies are the ones better situated to obtain devices with internal micro and nanofeatures. If the Internet of Thing is going to bring us billions of sensors, they will be probably small, and, consequently, the harvesters/batteries supporting their energy needs should also be small. However, the only way of capturing enough energy from low density harvesting sources with such small devices is that those devices have high internal features density (for instance 3D internal architectures where to integrate large surface-to-volume ratio nanomaterials if need be). Silicon technologies are also the only ones producing (by means of micromachining) small scale free surfaces and volumes that allow those devices to effectively couple to environmental stimuli.
SiNERGY context (2): off-grid energy autonomy
As we know, off-grid energy autonomy is one of the most demanded functionalities since it enables a wide range of interesting disposable, portable and deployable applications. In all these cases, energy is usually provided by batteries. SiNERGY focuses in deployable solutions, where periodic battery recharge or replacement will be unpractical when faced with such a large number of devices.
Energy harvesting, tapping onto environmental sources of energy, such as vibrations or waste heat, can be a way of directly powering the sensors, or keeping continuously charged an auxiliary battery that will be a pretty universal energy autonomy solution.
SiNERGY objectives
Thermoelectric harvester
Since waste heat is one of the most recurrent environmental energy sources, one of the harvesting options considered is the development of a thermal microharvester, which given the philosophy of SiNERGY will be attempted using silicon technology friendly materials and architectures. High density features are needed to overcome the trade-off of silicon being an enabling technological material but a poor/modest thermoelectric material
The main objective, for this purpose, is:
• the integration of silicon based nanowire (NW) arrays as thermoelectric material into a silicon micromachined structure. This structure shall enable an internal thermal contrast to develop between two isolated silicon regions, which once bridged with the Si NWs, will be the basis of an all-silicon microthermoelectric generator.
Intermediate objectives for achieving this goal are then:
• Obtaining high density arrays of (arbitrarily) long nanowires at wafer level, considering different bottom-up and top-down synthesis/definition processes
• Obtaining a microstructured platform with compact quasi three-dimensional features with two distinct areas of thermal contrast, one in contact with the silicon bulk, the other in contact with a microradiator to be integrated on top.
• Devising a fabrication technological route that makes compatible the integration of above three elements (Si NWs, microplatform, microradiator), and enable power output densities in the 10-100 μW/cm2 range
• Avoiding the use of extreme lithography / nanolithography in the process sequence, thus decreasing the technological complexity and cost of the resulting devices and easing their large-scale replication
• Choosing an architectural arrangement in which the arbitrary long, high density nanowires arrays are integrated in the microstructure platform in a way that good thermal and electrical connection is assured at no extra technological cost.
Mechanical energy harvester
Another possibility of energy harvesting is using mechanical energy, e.g. vibrations. There are three main methods to convert mechanical energy into electrical energy: electromagnetic, piezoelectric, and electrostatic. For many small autonomous sensor systems, miniaturisation and cost effective manufacturability are important requirements. Silicon technology is the way to go to reach those requirements, but this rules out the use of electromagnetic transduction - It turns out to be virtually impossible to efficiently scale down and integrate pick-up coils and magnets into silicon technology.
Therefore, SiNERGY focuses in:
• Developing electrostatic as well as piezoelectric energy harvesters based on Silicon technology with high power output and good reliability.
Intermediate objectives to achieve these goals are:
Electrostatic energy harvester:
• Material development and optimisation for silicon-based electrets (the polarisation source for electrostatic energy harvesters).
• Integration schemes for these electrets, with high surface voltages and long charge retention times (10 years @100°C) into out-of-plane mass-spring MEMS platforms.
• Device optimisation with increasing capacitance variation and minimizing parasitic capacitance. The power output goal for the electrostatic energy harvester is 500 mW for 1cm2 area.
• Reliable devices with shock resistance up to 5000 G.
Piezoelectric energy harvester:
• Fabrication of out-of-plane cantilever type Silicon MEMS structures
• Adaptation of compatible MEMS processes for reliable synthesis and integration of piezoelectric ZnO nano-objects onto silicon microstructures
• Device design which optimizes the strain/stress of nano-objects under short displacement vibrations, in order to achieve power densities beyond 25 mW/cm2
Solid State Li-ion microbatteries.
For the application of autonomous systems powered by harvesters, on-board energy storage devices are required to ensure a stable current supply and cover peak demands. In particular, lithium and lithium ion batteries (LIB) have the highest energy density of all known systems and thus represent the best choice for rechargeable batteries. Since liquid electrolyte based batteries present safety issues and limitations in size and design, pure solid state devices are gaining ground particularly for miniaturisation.
The main objective of this project is to develop high performing thin-film all-solid-state lithium-ion microbatteries compatible with silicon technology. In order to significantly increase the power density and capacity of the State of the Art microbatteries, a double approach based on improving kinetics of ion transport at the interfaces and increasing the effective surface area will be followed.
Two different architectures will be developed in order to face up the main goal of the project, namely:
• Thin-film planar structures to specifically implement strategies for improving ion transfer at the interfaces, i.e. current density, by multilayer deposition of all-based spinel microbatteries.
• Three-dimensional geometries to increase the current density, power capability and energy storage capacity by simply increasing the surface area.
In the planar configuration, performance will be the main target measured in form of rate capability (power) and lifetime (cyclability). In the 3D configuration, emphasis will be put on battery capacity (energy-density) and issues of mechanical integrity (reliability).
Intrinsically linked to the development of these two architectures, intermediate objectives of the project can be listed as follows:
• Deposition of defect-free thin-film electrolytes with high-enough ionic conductivity and reduced thickness (low internal resistance).
• Deposition of crystalline multilayers (cathode/electrolyte/anode) all-based on the spinel structure with continuous and smooth interfaces.
• Microfabrication of high density three-dimensional structures based on dry etched Si pillars fully compatible with silicon technology.
• Deposition of high quality conformal electrolyte/electrode multilayers (to be applied in 3D structured substrates).
Project Results:
Si NWs based micro thermal harvesters
Bottom-up approach
The bottom-up approach is based on the integration of arrays of Si NWs as active material in a previously fabricated Si microplatform able to endure the hard requirements of NWs growth process (high T). During SiNERGY project the efforts have been focused on the optimization of both elements, with the aim of increase the harvested power per unit area and accomplish the requirements foreseen for powering a wireless sensor node.
Si NWs optimization
The first goal in Si NWs development was the reduction of the high temperature required for the growth process, so as to limit the suffering and potential breakdown of Si microplatforms during the NW integration step. This was attained by changing the chemistry of the VLS process used for NWs growth, moving from silicon tetrachloride (SiCl4) to silane (SiH4) as silicon precursor gas. Process temperature was reduced from a 750-800ºC range to just 630ºC. The process was completed with the addition of diborane (B2H6) for ex-situ doping of the NWs and hydrogen chloride (HCl) to prevent the deposition of added polysilicon thin films.
Galvanic displacement method used for selective deposition of Au nanoparticles in bared Si walls (vertical <111> planes in trenches) was totally revised to allow a tighter control of nanoparticle size, the key parameter governing NWs diameter, and, therefore, overall array resistance. A comprehensive study determined how to use different process parameters to obtain statistical control of nanoparticle size distribution and deposition density. Cumulative count of NWs shows that mean diameter is 113 nm, and 80% of NWs have diameters between 76 and 207 nm; areal density of about 1 NW/µm2 is obtained with this optimized process. The required pre- and post-processes involving wet steps were adjusted for suitability with new microplatforms.
A complete set of test structures, and specific measurement methods were developed to determine the material properties of NWs. Electrical and thermal conductivity and Seebeck coefficient were measured making use of ad-hoc test structures for single or several NWs. Values obtained, 200 S/cm for electrical conductivity, 6.5 W/m·K for thermal conductivity and 331 μV/K for Seebeck coefficient result in a figure of merit ZT≈0.11 for Si NWs used as thermoelectric material in bottom-up based μTEGs, obtained with NWs with a 113 nm mean diameter. This ZT value exceeds that of bulk silicon by a factor of 10 and is the first reported for Si NW arrays epitaxially integrated in micro-thermoelectric harvesters. The thermal conductivity was determined with a novel method based on thermal AFM and fitting to a thermal model.
Si microplatform optimization
The key goal in the development of Si microplatforms was the improvement of the thermal isolation between hot and cold parts to boost the thermal gradient obtained from a waste heat source. New designs implemented in SiNERGY kept the use of successive trenches to attain a longer effective NWs length between hot and cold parts, and introduced a new type of low thermal conductivity supports for the metal lines. In this way, after Si NWs integration, microplatform parts are linked only by thermocouple active materials, avoiding other parasitic heat paths. The designs adopted for these parts allow arbitrarily long features, which can be dimensioned to the optimal values required by the Si NWs properties.
The Si microplatform fabrication process was revised to enhance power levels provided by μTEGs. The metallization and the metal-Si contacts were improved in order to not degrade the low internal resistance provided by the dense Si NWs arrays (large amounts of highly B doped Si NWs connected in parallel). TiW was selected for electrical interconnections, using a preceding boron doping step and a subsequent thermal annealing process to ensure the formation of a silicide layer in contact areas.
The thermal contact with the environment (heat removal in the cold side) was identified as the key limiting factor in performance. A process was envisaged to fabricate a thermal interface structure in current devices, linking the isolated suspended platforms with a standard metallic thermal heat dissipater. Although integration was not yet accomplished, conservative estimates show that demo application power targets can be attained using a reasonable device area (a few cm2 at most).
Other advances adopted in the course of SiNERGY project, both on the design and fabrication of the Si microplatforms, were intended to increase production yield. The platform robustness was enhanced using thick Si bars to hold the suspended platform in the most critical phase, i.e. before the integration of the Si NWs. The membranes supporting the metal connections were redesigned to match with square apertures for the DRIE in the backside, leading to a steadier etch process. The passivation thickness was increased and a partial etch was performed in bond pads location to avoid the exposure of whole metal surface after NWs integration. Finally, the whole fabrication sequence was rearranged to avoid the critical interferences between the different micromachining steps involved.
µTEG performance
The integration of improved bottom-up Si NWS into silicon micromachined platforms was achieved, and harvested power with resulting μTEGs was assessed in different conditions. Measurements performed in still air show low thermo-voltages (hundreds of μV) comparable to the Seebeck coefficient measured for Si NWs arrays. Thus, in this condition the delta T achieved from the hot surface is in the 1-5 °C range, resulting in quite low harvested powers (10 nW. Therefore, the integration of a heat exchanger seems to be mandatory for having efficient devices. However, measurements performed using forced convection to emulate the effect of a heat exchanger provide a delta T in the 10-40 °C range, still lower than values attainable with a passive heat exchanger according to simulations).
Data obtained with forced convection (showing a voltage increase of 8 times when compared to still air), allow the estimation of the power expected from such devices in realistic operative conditions. The 2nd generation best samples show maximum generated powers around 0.07 µW from a device surface of 4 mm2 (1.75 μW/cm2) with open-circuit voltages around 3 mV, obtained with a hot-surface temperature of 120 °C. Thus, the ≈ 10 µW target needed for practical application on demo scenario can be basically reached with a device area of 2.5×2.5 cm2.
Future development
Despite the appropriate results achieved with the bottom-up μTEGs developed in SiNERGY, in line with the power requirements agreed for an autonomous wireless sensor node, there is still room for performance improvement. Future efforts will be focused on the integration of proposed heat spreader element in current microplatforms, in order to remove heat from cold parts to the ambient and procure a higher delta T from available waste heat sources. The design of the microplatforms can also be optimised in terms of power density, which in current devices was waived to allow the integration of the self-test heating element. There is also room for improvement of the active material ZT. Work will focus on a further reduction of the NWs diameter to approach the 50 nm target, to get an extra reduction of NWs thermal conductivity. Other active materials with potential better thermoelectric properties, like the SiGe, will be investigated to be used with the bottom-up VLS growth process. This activity will be conducted in the framework a national research project recently granted by Spanish Ministry of Economy and Competitiveness.
Top-down approach
In the top-down approach, lateral architectures (using silicon NWs) were obtained. Lateral thermoelectric harvesters were designed to be fabricated in stacks, enclosing LPCVD grown poly SiNWs within a SiO2/Si3N4 mould. Heavily doped p- and n-type polysilicon legs were fabricated. Multilevel arrays of such NW (pairs of 3 level stacks) were closely packaged (separation of about 300 nm).
Tests were carried out on to evaluate the yield of the manufacturing process and the thermoelectric properties of the fabricated nanostructures. In the first-generation top-down devices the electrical resistance was found to scale correctly with the number of nanowires in parallel. Moreover, from the measurements, resistivity values were found typical of the high-doping range (around 1020 atoms/cm3) required for high-performance thermoelectric conversion. Specific test structures were utilized to estimate the Seebeck coefficient of the n and p-type NWs. An approximately linear growth of the Seebeck voltage with the temperature difference was obtained. The Seebeck coefficient of the nanowires was around 150 µV/K for both doping types, as expected considering the high-doping level of these nanostructures.
Simulated tests of operation were also carried out using a hotplate to check the produced thermoelectric voltage in conditions close to the real application foreseen for the devices, using a commercial radiator fixed using a special double-side adhesive tape sold with the radiator. Devices appeared to promptly respond to the temperature variation, with produced voltage in the order of 300 mV for heating temperatures as low as 80 °C.
The weak point of the first-generation devices was the fabrication yield, showing a critical at the wafer-boding step. However, numerical simulations showed that the performance gain using vacuum packaging was significant only for NW stacks with a high number of levels. On the contrary, for stacks of nanowires composed by a reduced number of levels, the performance of the device working in air can be comparable if not better than the vacuum packaged devices. This enabled a major simplification of the manufacturing process. The process flow could be modified by replacing the wafer bonding procedure with a plain SU-8 lithography followed by a backside etching of the entire thickness of the substrate up to the membrane constituted by Si3N4, SiO2 and by the nanowires. This made the dielectric membrane containing the nanowires more robust, allowing to mount on it a metal heat sink. A commercial anodized aluminium heat sink could then be fixed manually on the suspended masses, achieving high fabrication yields.
The conversion rate of the second-generation top-down devices was tested under simulated operative conditions. A maximum generated power around 0.16 µW from a total device surface of 0.64 cm2 (0.25 μW/cm2) with an open-circuit voltage around 3 V was obtained at a hot-sink temperature of 120 °C. Thus, the target of ≈ 10 µW needed for the practical application on the demo application is basically reached with an exchange area of 6.3×6.3 cm2, also considering that the modification of the doping process for n-type nanowires allowed to obtain a ≈ 10× reduction of the electrical resistance of the devices.
Mechanical energy harvesters
Electrostatic approach
Layout, materials and process flow of the 1st generation electrostatic devices
The basic configuration of an electrostatic energy harvester consists of five key elements: a seismic mass, suspension/springs, a set of electrodes, a charged electret and a packaging. We chose an in-plane sliding capacitor with a large usable mass and electret/electrode area and thus potentially the largest output power.
The active part of the harvester consists of a variable capacitor, created by two sets of interdigitated electrodes on the bottom glass wafer (W1) and the charged, patterned electret on the Si wafer (W2). This ensemble is sealed with a top glass wafer (W3). Upon movement of the mass, the overlap (capacitance) changes periodically, resulting in a generated AC output voltage. The flexible springs allow for an in-plane movement of the mass. The micro-fabrication possibilities in bulk silicon, together with its high stiffness and low susceptibility to fatigue, make Si the ideal material to fabricate the springs. The mass and the spring system can therefore be integrated in the one Si wafer. Important for the long term functioning of the harvester is the stability of the electrostatic charge on the electret. We chose for an inorganic SiO2/Si3N4 layer because of the good charge retention and for patterning of the electret by pre-structuring the substrate by DRIE prior to the deposition of electret layer. This has as major advantage that the nitride layer is continuous, which eliminates the possibility of charge diffusion.
Apart from carrying the capacitor electrodes, the packaging has different functions: first, it provides protection for the (fragile) Si mass/spring structure, limiting the out-of-plane mass displacement and therefore increasing the reliability. Second, in case of a hermetic vacuum packaging, the lifetime of the electret is extended by excluding influences from moisture and third, the vacuum eliminates the power loss due to air damping during mass movement. We chose to use a wafer-scale adhesive bonding process, where in case of the W1-W2 waferbond, the structured adhesive polymer also defines the capacitor distance. A stepped dicing process allows access to the electrodes on the bottom wafers. The 1st generation devices were successfully produced via the described route. The output power of the devices was measured using a shaker setup with sinusoidal input vibrations, showing the characteristic resonance curves of output power versus frequency, and a quadratic relation between the output power and the input acceleration. The maximum generated output power was in the order of 600 µW for an input acceleration of 3.5 g (maximal mass amplitude) at a resonance frequency of around 1100 Hz.
Improved 2nd generation electrostatic energy harvester layout and process flow
Although successful in terms of output power, the thin silicon springs of the 1st generation devices were mechanically not robust enough for the targeted application in a TPMS. Improving the mechanical reliability was therefore the main point for the 2nd improved device generation, to facilitate the ease of integration in the TPMS. The most important changes in device layout and process flow were:
- Integration of the flexible silicon stoppers to improve the shock resilience. These could be integrated in the device layout using the two existing DRIE steps for the Si wafer (electret etch and spring etch) without adapting the processing.
- Integration of cavities with dimples in the capping wafers, reducing the out-of-plane movements of the mass, while maintaining the freedom of movement.
- An improved waferbond between the bottom capping wafer with electrodes and the Si device wafer with the electret: replacing the lithographically patterned thick BCB bond polymer by a thin layer of SU-8 around the cavity in the capping wafer, results in an increased bond strength (reliability) and simultaneously improves the hermeticity of the device, providing a better vacuum (output power) and moisture barrier (lifetime).
These proposed layout and processing improvements were all successfully implemented during the fabrication of a batch (5 wafers) of 2nd generation electrostatic energy harvesters, resulting in a high yield and devices without visual errors.
2nd generation electrostatic energy harvester device characterization
Devices mounted on PCB were characterized on the shaker setup sinusoidal input vibrations and the output power was determined using the generated AC voltage signal, as well as in DC mode by charging a storage capacitor after rectification. The devices showed a power output of up to 700 µW at 0.5 g input acceleration. While this level of output power was comparable to the 1st generation devices, the low input acceleration necessary to obtain this, is remarkable. Due to the high vacuum SU-8 waferbond, the energy loss due to air damping was reduced and the sensitivity of the 2nd generation devices increased dramatically (3000 vs 50 µW/g2).
For a more application oriented characterization, band-limited white noise with a PSD in the range of what is to be expected in a car tire (10-4 to 10-2 g2/Hz) was used as input on the shaker system. The generated output power increased from 30 µW for the 1st generation devices to almost 200 µW for the improved 2nd one.
In conclusion several reliability improvements were integrated in the layout and in the process flow for the 2nd generation electrostatic energy harvesters, leading not only to mechanically robust devices, but also to very low losses due to air damping. As a result, the 2nd generation devices are very sensitive, which means that already at low driving speeds, sufficient output power for the TPMS application will be generated.
Piezoelectric approach
Layout, materials and process flow of the 1st generation of piezoelectric harvesters
Piezoelectric material has the property of generating a voltage along it when mechanically strained. It is well-known that microelectronic technology can be used to build tiny mechanical structures able to move and interact with integrated electronics. With these two premises, we have been working on the development of energy harvesters compatible with silicon technologies. The use of novel piezoelectric nanostructures and the way of easing their integration with silicon have been explored in this project. In our case, the configuration selected for the energy harvested is based on a cantilever structure, covered by the piezoelectric material, with a tip mass. However, in contrast to the electrostatic case, the work done in this project about piezoelectric technology has been more focused on discovering these new materials than in obtaining an operational device.
From the point of view of materials, we have invented a way to control the selective-area growth of ZnO planar nanostructures. They can be grown much faster than the typical nanowire, better reproducibility and high quality and coverage. An electrochemical method to activate gold seed layer has been also created to improve the reproducibility and uniformity of the growth of nanowires.
An in-depth characterization including, SEM, TEM, XRD, in-situ picoindentation and piezoresponse AFM have been carried out with excellent results. In addition, the following three hybrid devices were developed to gather an independent knowledge on the MEMS structure, the piezoelectric nanomaterial and polymer encapsulation and electronic integration:
AlN-based device mounted on an ad-hoc PCB:
The same MEMS technology and identical design have been used to fabricate a piezoelectric energy harvester of 25 mm2 based on an AlN thin-film. A generated voltage of 0.2V at a resonant frequency of 688 Hz was measured for an acceleration of 0.1G and a load resistor of 1MΩ.
Flexible generator based on ZnO NS embedded in polymer:
The piezoresponse of the whole structure comprised of metal-polymer-ZnO-AlN-metal has been measured by PFM (Piezoresponse Atomic Force Microscopy) obtaining an effective piezoelectric coefficient of 2.7 pm/V. Also, in order to demonstrate the capability of using ZnO NSs for energy harvesting, a flexible test structure comprised of a stack of metal-polymer-ZnO-AlN-metal was fabricated and characterized under periodic bending and a constant vibration.
cm-scale energy harvester based on PDVF and attached tip mass:
We have manufactured several devices based by integrating PVDF, polystyrene, silver ink, acrylic adhesive, and epoxy. The 1st generation prototype had a resonance frequency around 32 Hz, a maximum RMS open-circuit voltage of 17.5 V at an optimum load resistance of ~10 MΩ, and a generated power of ~30 µW for an input harmonic acceleration of 1 G. It can be translated to a power density of ~10 µW/cm 3. Thanks to an optimized design, the new prototype exhibits a resonance frequency of 50 Hz, a peak-to-peak voltage of 80 V with a load resistance of ~10 MΩ for an input harmonic acceleration of 2 G. It can be translated into a generated RMS power of ~80 µW (more than 4 times higher).
Layout, materials and process flow of the 2nd generation of piezoelectric harvesters
A batch of 8 wafers with piezoelectric energy harvesters has been just fabricated according to the improved 2nd generation device architecture and process flow. Several optimizations have been performed regarding the designs of the 1st generation devices:
- 90-degree corners have been filleted to avoid lines of high stress that could lead to premature fracture at resonance.
- Dependence between mass-beam lengths has been optimized to maximize power output.
- Several novel designs with multifrequency resonance or tri-axial motions have been added.
- A frame patterned by DRIE has been defined around each chip perimeter to allow the dicing of the wafer with tweezers.
In addition, several process versions have been run in parallel. Specifically, a simplified run has been used to create MEMS platforms with the same designs but without piezoelectric layer or top electrode. This allows performing the deposition of the ZnO nanostructures and the protective polymer by means of a hydrothermal growth followed by inkjet printing of SU8 and silver/gold inks.
Preliminary experiments show a good covering of the NSs, good adhesion of the SU8 to the wafer, and successfully metallization of the SU8 top surface with silver ink to create the second electrode.
In conclusion, several process versions have been run in parallel including a simplified run which will results in the creation of MEMS platforms that allows depositing the piezoelectric layer and the top electrode as post-processes by using hydrothermal growth followed by inkjet printing of SU8 and silver/gold inks. This is considered a highlight of the project since it may lead to a great simplification of the fabrication of such devices. These devices and their characterization will be finished after the project, but in the meantime several hybrid prototypes have been characterized: (1) AlN-based device mounted on an ad-hoc PCB with a power of 0.2 µW for 0.1 g of acceleration, (2) a flexible generator based on ZnO NS embedded in polymer, measured by PFM to obtain an effective piezoelectric coefficient of 2.7 pm/V and (3) an cm-scale energy harvester based on PDVF film and attached tip, with an RMS power of around 130 µW (and 76 Vpp) at 2 g for an optimum load impedance of 10 MΩ. The team responsible has secured the follow-up of these developments through a recently granted a new project (ENSO –Energy for Smart Objects of the ECSEL JU).
Thin film solid state batteries
LiMn2O4 based battery
LiMn2O4 (LMO) has been first considered to be used as an intercalation electrode for a high voltage cathode material. This material has been grown using RF-sputtering, pulsed laser deposition (PLD) and a solid state reaction (SSR) process. The material holds a theoretical capacity of around ~154 mAh/g and an outpum voltage of 3.5-4.5V. Thin layers of LMO have been characterised in detailed within the SiNERGY project. IMEC has prepared LMO films through RF-sputtering to be considered for full stack planar battery cell development and through electrochemical deposition of MnO2 and post-lithiation conversion through SSR which is a compatible process towards a 3D solid state battery cell assembly. IREC has fabricated LMO layers trough PLD.
Planar full-stack battery cells were fabricated. Battery stacks based on LMO cathode electrode, LiPON solid electrolyte and Lithium anode electrode have been characterized and tested. This thin film solid state battery stack shows 92% of the theoretical capacity. This battery stack delivers a potential of 4.1 V and can achieve a power of 0.24 mWh/cm2 at 0.1 C rate. The battery stack is encapsulated in a 2 x 3 cm glass. The encapsulated battery is taken out of the glovebox to ambient air and still an open circuit potential of 4.1 V can be measured.
IREC has explored a novel approach for the fabrication of a full battery stack exploiting the exceptional capabilities of the spinel LiMn2O4 optimized cathodes. This advance is presented here as an alternative full battery stack, which can be useful in some applications due to its extremely fast performance and simplicity of fabrication. The stack is formed by a LiMn2O4 cathode, aqueous liquid electrolytes (that do not have the safety drawbacks of organic electrolytes) and Zinc foil. The thickness of the battery based on its three components (cathode, separator and anode) is lower than 30 µm, considerably inferior to the 500 µm of the silicon substrate. A full cell comprising 1 µm LMO as cathode, a Zn foil with 1 µm of thickness as counter electrode and a Celgard separator with thickness of 25 µm soaked with 1 M Li2SO4: 20 mM Zn SO4 solution, was tested.
The capacity of this cell reaches a value of 50 µAcm-2 under a current rate of 0.7 C (the cell is cycled in less than 42 minutes). The cell maintains 70% of this capacity after an increment of the current rate of 43 times, (the cell is cycled in less than 2 minutes). The potential delivered by the battery is close to 1.9 volts because to the contribution of the LMO cathode and Zn anode electrodes.
Li4Ti5O12 based battery
Li4Ti5O12 (LTO) is a competitive candidate as an electrode material for Lithium ion batteries since it has a stable operating voltage vs lithium (1.55V) very small structural change (negligible volume expansion) and it can be easily obtained by several routes. IMEC has prepared LTO films through RF-sputtering to be considered for full stack planar battery cell development and post-lithiation conversion of TiO2 which is a compatible process towards a 3D solid state battery cell assembly, IREC has fabricated LTO layers trough pulse laser deposition.
Planar full-stack battery cells were fabricated. Battery stacks based on LTO cathode electrode, LiPON solid electrolyte and Lithium anode electrode have been characterized and tested. In order to increase the capacity of the battery, LTO thicker films have been used to develop a full battery stack. 500nm LTO films have been deposited by means of RF-sputtering. The electrochemical performance of this stack has been studied. Cyclic voltammetry shows the characteristic peaks for LTO and charge/discharge cycles show a flat plateau at 1.55V. This battery stack achieves full theoretical capacity at 1C. At 10 C rate (300 μAh/cm2) the battery stack reaches 50% of its capacity with a 99% coulombic efficiency. This battery stack delivers a potential of 1.5V and for the first battery stack delivered we could achieve a power of ~0.225 mWh/cm2 (500nm LTO film).
3D thin film battery proof of concept
For 3D geometries and Si compatible stacks several materials have been investigated in order to explore conformal depositions and post-lithiation of individual films towards a 3D solid state thin film battery. The 3D architectures contemplated are based on a hexagonally arranged array of Si pillars etched into the Si substrate with pillar diameter of 2 µm, an inter-pillar distance of 2 µm and a pillar length between 60 µm-100 µm.
Lithiation schemes have been established for electrode layers. Manganese Oxide, MnO2 (~3 V) has been used to do a post-lithiation step through a solid state reaction (SSR) to create LMO electrode layers (~4.2 V). The growth of the initial films is done through 3D compatible deposition techniques called Electrochemical deposition (ECD). Film deposition and post-deposition lithiation of individual thin films and half cells were evaluated in planar geometry. Moreover, MnO2 has been deposited conformally in 3D geometries with high aspect ratio and has proven to be a well suited material to work as a positive electrode material for the next generation thin film batteries. This LMO electrode has shown promising results to be used in 3D micro-batteries. Recent results have shown that MnO2 can be easily platted on 3D structures showing good conformal deposition and electrochemical behavior. ECD MnO2 film LMO grown on 3D pillar structures have been successfully converted into LMO by post-lithiation. The 3D electrode arrangement shows an enhancement of a factor of 20 compared to a planar LMO thin film of the same thickness (~350 nm).
The preparation of conformal electrolyte layers through a solid state reaction (SSR) have shown to be challenging. LiTaO3, Li2NiGe3O8 and Li4Al4-3xSiO4 electrolytes have failed to provide the ionic conductivity and morphology needed for battery stack development and for 3D structuring. For planar thin film batteries SiNERGY has considered the solid electrolyte Lithium Phosphorous Oxynitride (LiPON) as backup material. This material is at the moment not compatible for 3D thin film battery technology. Hence, it is not trivial to think of an adequate solid state electrolyte which shows conformality and high ionic conductivity. At this point, IMEC has taken the knowledge they have in battery technology and specially in solid composite electrolyte (SCE) components and has implemented this type of materials within the SiNERGY project as an alternative. The SCE is based on a matrix which conducts Li-ions very easily and can be used as a filler for the 3D pillar arrays. This approach has led to a 3D thin film proof of concept device: LMO/SCE/Li (~4.2 V).
Feasibility integration in application scenarios
Fully autonomous tire pressure monitoring system (TPMS) demonstrator
Tire pressure monitoring systems (TPMS) are mandatory in USA and Europe in new cars since 2008 and 2012 respectively. The main parameters to sense are pressure and temperature of the air inside a tire. The measurement frequency depends on how fast is necessary to detect a possible puncture; usually a 5 to 10 second measurement rate is acceptable. For the autonomy of this TPMS demonstrator vibrations and shocks generated at the inner-liner of the tire will be used. There are two reasons to transfer from the standard TPMS on the valve to the inner-liner of the tire: much higher vibration levels and possible added functionality beyond pressure, resulting in a so-called ‘intelligent tire’. Small, cheap and robust vibration energy harvesters made with silicon processing are used to obtain autonomy without using batteries.
The electrostatic vibration energy harvester developed by Imec-NL was combined with the ultra-low power TPMS module of STE. The module did not contain a battery and only the power generated by the harvester was used. The energy harvester improvements obtained in SiNERGY resulted in higher power generation at lower excitations and much better reliability. Especially, the reliability is known to be the challenge of using brittle silicon in applications with high impact shocks. Shocks in the tire at normal driving conditions can already amount up to 150 G for 60 km/h. Much higher accelerations can occur during driving on e.g. bad roads and TPMS integrated in the tire should withstand acceleration exceeding 2000 G. The silicon based harvester was improved by optimizing the springs and introducing efficient damping by introducing flexible silicon bumpers. Such 2nd generation devices with reliability improvements do not break up to 2000 G.
The system was tested in the lab and was fully operational at very low vibration levels. At those low vibration level (~10-4 g2/Hz) the pressure was measured and sent every 10 seconds. The power needed was only ~4µW!! It scales linearly with noise level and at 2 times higher level, the pressure measurement was sent every 5 seconds. This result was possible due to development of STE’s ultra-low power TPMS module and the improvements on the energy harvester.
Thermal electric generator (TEG) demonstrator
The temperature measurement in Foodservice Industry is extremely important for two reasons:
i. Food safety. Time and temperature are the two most important factors to control and monitor in the prevention of food borne illnesses.
ii. Quality and performances. Temperature is a parameter equally critical to obtain the desired quality of the cooking. For perfectly fried foods, it is critical to keep the oil at the correct temperature.
Industrial fryers are gas-powered, unplugged industrial appliances. EC regulations require oil quality to be monitored using a log of oil temperature as a function of time. Thermal harvester may then supply the power needed to monitor oil temperature and to transmit data through a wireless connection to a remote data logging system without the burden of wiring the fryer to the electric net. The industrial fryer was used as a waste heat resource for a commercial in order to test the feasibility of the system.
The signal is transmitted by an ultra-low power 434 MHz RF module with pulse-based transmission, provided with a microcontroller from MSP430 family. A J-type thermocouple was used as a temperature monitor connected directly with the microcontroller. Integration tests were performed to anticipate assembly issue that might show up at the module level in the demo application using a commercial off-the-shelf TEG by Marlow Inc. using Bi2Te3 thermoelectrics with a nominal power output 5 times larger than the SiNERGY top-down thermal harvester. They led to identify the optimal hot point on the fryer metallic framework to be used to collect heat, to set a proper module assembly, and to define a suitable heat dissipation strategy. Results showed that the assembly allowed the RF transmitter to be powered and to transmit data with a frequency larger than 0.5 Hz with less than 5 seconds of initial latency without any need for a battery to accumulate power. This implies that the SiNERGY thermal harvester may provide a sufficient power output out of a surface of about 60 cm2, largely compatible with the available hot wall size. Tests also provided clear evidence of the importance of an efficient heat dissipater to prevent temperature equilibration across the TEG after a few minutes of operation.
Piezoelectric energy harvester (PEH) demonstrator
Finally, a third integration exercise has been performed to cover one of the use cases projected at the beginning of this project. This use case focused on predictive maintenance, which is a novel concept on industrial maintenance based on the idea of predicting a machine failure before it occurs by means of the monitoring of several parameters, such as vibrations or temperature, to find precise patterns that are faithfully related to the imminent failure. Therefore, the environments of application are industries, factories or vehicles, where ambient vibrations are present. Therefore, we decided to use vibration-driven piezoelectric energy harvesters to cover this application.
The technology used to fabricate this demonstrator is based on piezoelectric polymer, instead of a silicon based devices, due to the higher degree of maturity and higher power generation. We have used a kit EZ430 (Texas Instruments), which contains a full-equipped sensor node with wireless connection and different sensors (temperature, pressure and 3-axes accelerometer). Several power management circuitries have been utilized to rectify and manage the power scavenged. The choice of using one or other depends on the application. Basically, the current generated has to be rectified, the charge accumulated and the subsequent voltage adapted to the requirements of the node of application.
We have configured a characterization setup that allows applying controlled vibrations to the energy harvesters. The energy harvester has been designed to resonate at 50 Hz, obtaining a peak-to-peak voltage of 80 V for a load resistance of ~10 MΩ, and an input sinusoidal acceleration of 2G. Therefore, this means a generated RMS power of ~80 µW. After using a power management circuit, an effective power of 22 µW can be generated, corresponding to an efficiency of ~20%. It allows the operation of the EZ430, which requires less than 100 µW for a normal operation of waking-up, sensing, transmission and going to sleep mode again. For instance, for the case of the rotor of a helicopter or the train wheel set, where a vibration of around 20-60 Hz and 1-2G is present, 1 min of charge will allow 1 second of operation, which should be enough to allow continuous unassisted operation of the node.
Potential Impact:
SiNERGY focuses on silicon and silicon friendly materials and technologies to explore energy harvesting and storage concepts for powering microsensors nodes. SiNERGY selects a series of relevant examples of power microgeneration and storage (thermoelectric generators, mechanical harvesters and microstructured batteries) with the aim of pushing them further into their development and performance maturity. With that goal in mind, emphasis is placed on thin films and nanostructured materials and their integration route into a technology able to bring the eventual solutions closer to an exploitable phase. For this reason, we consider silicon technology compatible materials as our starting point. Silicon technologies provide an enabling path to miniaturization, 3D architectures (improved energy densities), mass production with economy of scale, and the ability of power intelligence integration. Harvesting energy, tapping into environmentally available sources such as heat and vibrations, may be a good solution in man-made scenarios applications. 10-100 μW/cm2 seems appropriate for many such applications. Coupling those harvester devices to secondary batteries to buffer enough energy to account for the power demand peaks required by the communication unit of wireless nodes would be an enabling energy autonomy solution.
Energy autonomy keeps being one of the most desired enabling functionalities in the context of off-grid applications, such as wireless sensor networks (Internet of Things, Trillion Sensors). Micro and nanotechnologies have already made possible the fabrication of small, low cost and good performance sensors that are called to be protagonists of continuous monitoring scenarios and distributed intelligence paradigms. Such technologies are the prime candidate for building microenergy solutions of similar robustness able to power such sensors during their whole lifetime.
Even though SiNERGY focuses in the materials and technologies leading to harvesters and storage devices, attention was paid to real applications scenario. As a consequence, while the focus is placed on the devices themselves, system level integration issues have been considered as well, to keep in mind application-wise all the elements required by an eventual autonomous working sensor node, and to consider which of them may have an impact in some of our device architectural choices.
SiNERGY results and exploitation scenarios
During its lifetime, SiNERGY project produced several results in terms of advancement of knowledge (14 items) / preliminary foreseen commercial exploitation (four items) in the field of microdevices for energy harvesting and storage (See the PUDF section for more details). Also four patents are at different stages of submission, namely:
(1) System and device for collecting piezoelectric energy // submitted by CSIC // WO2016ES70381
(2) Method for fabricating Solid-State Thin Film Batteries // submitted by imec // EP16168461 – US15146714
(3) Bioelectonics device based on piezoelectric and magnetostrictive materials for cellular interaction and neural stimulation // in process, by CSIC // EP16411241 (preliminary number)
(4) Method for forming Lithium Manganese Oxide Layers // in process, by IMEC
These results have been gathered in five major findings), or Key Exploitable Results (KERs), in order to better describe the potentiality behind their exploitation, and to explore the impact that such new material solutions for low-cost, miniaturized and environmentally friendly applications can have on societal and economic issues. It is worthwhile noting that the combination of any of those KERs configures, actually, all the possible SiNERGY microenergy solutions:
KER1 - Microenergy solution based on a thermoharvester (bottom-up design)
KER2 - Microenergy solution based on a thermoharvester (top-down design)
KER 3 - Microenergy solution based on an electrostatic mechanical harvester
KER4 - Microenergy solution based on a piezoelectric mechanical harvester
KER5 - Thin film micro-battery
Short SiNERGY KERs’ descriptions are reported below, with a sketch on their innovativeness and unique selling proposition.
A collaborative risk analysis with focus on key risky factors has been performed. Risk matrices are reported for each KER, describing, for each different source of risk, the success of the potential/provided intervention and the related risk grade.
A self-explicative synoptic table, which condenses in a glance the expectations and the nature of the activities foreseen for the project results by each of the consortium partners, is also presented within each KER’s paragraph.
In relation to the role of the companies of the consortium, it must be said:
- Manufacturing energy harvesters is not the core business of Electrolux, but it is firmly convinced that Autonomous Energy Efficient wireless sensors powered by low-cost energy harvesters may find a place in Smart Appliances produced by Electrolux, and in predictive maintenance schemes in Electrolux production facilities.
- STE is deeply interested in energy harvesting as a complement to its micro.sp communication technology for wireless sensors networks. However, manufacturing energy harvesters is not the core business of STE, and only if such harvesters were commercially available at high numbers/low cost STE may consider market operations in the Autonomous Energy Efficient Wireless Sensors field as part of the value chain.
KER1 - Microenergy solution based on a thermoharvester (bottom-up design): this is a solution for energetic autonomy based on a microthermoharvester (with bottom-up silicon nanowires as thermoelectric material) with appropriate power management. It does not need primary batteries or wired power. The innovativeness stands in the production of harvesters using silicon nanowires as thermoelectric material, built following a monolithic approach that uses high-density integration of nanowires by means of bottom-up techniques. Unique selling proposition: this harvester is a combination of microdevices built with materials and processes compatible with silicon technologies (scalable technologies, with size/cost reduction) following a technological path of low complexity. It requires the employment of low-cost, geo-abundant, environmental-sustainable, and non-poisonous raw materials. It should be moreover considered that, as will be showed in the section “Social and economic implications”, that energy extracted from waste heat sources is contained in the device’s application scenario.
KER1 Expectations Table
Manufacturing, Realisation: CSIC, IREC
Assembly: ELUX
Research: CSIC, CERR, ELUX, IREC, STE, UNIMIB
Consultancy, Training: CERR, STE
Utilisation in other business: CERR, STE
Saling, distribution: --
Services: --
KER2 - Microenergy solution based on a thermoharvester (top-down design): this is solution for energy autonomy based on a combination of microthermoharvesters (with top-down silicon nanowires as thermoelectric material) with appropriate power management. It does not need primary batteries or wired power. The innovativeness stands in the production of harvesters using silicon nanowires as thermoelectric material, built following a monolithic approach using medium density integration of nanowires by means of top-down techniques. Unique selling proposition: the technology is a combination of microdevices built with materials and processes compatible with silicon technologies (scalable technologies, with size/cost reduction, and with abundant material). It uses inexpensive, geo-abundant raw materials, indeed. As for the previous KER, this technology may use energy extracted from waste heat sources too.
KER2 Expectations Table
Manufacturing, Realisation: CNR
Assembly: ELUX
Research: ELUX, STE
Consultancy, Training: CERR, STE
Utilisation in other business: CERR, STE
Saling, distribution: --
Services: --
KER 3 - Microenergy solution based on an electrostatic mechanical harvester: this solution is an energy autonomy solution based on a combination of electrostatic MEMs-based mechanical harvesters. As for the previous technologies, it does not require primary batteries or wired power. The innovativeness of the solution stands in the small size, the monolithic approach, the improved reliability and in the improved moisture resistance of the device. Unique selling proposition: this is a combination of microdevices built with materials and processes compatible with silicon technologies (abundant material, scalable technologies, with size/cost reduction). The application scenario considers, additionally, the use of energy extracted from vibrational and/or shock sources.
KER3 Expectations Table
Manufacturing, Realisation: --
Assembly: --
Research: imec-NL, STE
Consultancy, Training: CERR, imec-NL, STE
Utilisation in other business: CERR, STE
Saling, distribution: --
Services: --
KER4 - Microenergy solution based on a piezoelectric mechanical harvester: this microenergy solution is based on the employment of different piezoelectric energy harvesting technologies. Its innovativeness consists of a monolithic integration of an energy harvester, rectifier diodes and an intermediate storage capacitor. It uses ZnO nanostructures and polymer layer as piezoelectric layer, with a remarkable robustness increase. Unique selling point: the presented solution is a monolithic solution, with a smaller size, a higher integration and a cost reduction. Nanostructures are employed instead of thin-film, conferring higher robustness, and opening wider application scenarios. In-situ rectification/storage means the possibility of building arrays, which results in higher power, broader vibration spectrum and higher efficiency. Use of flexible substrates, moreover, implicates more robustness, lower resonance frequency and low cost.
KER4 Expectations Table
Manufacturing, Realisation: CSIC
Assembly: CSIC
Research: CSIC
Consultancy, Training: CERR,
Utilisation in other business: CERR
Saling, distribution: --
Services: --
KER5 - Thin film micro-battery as a stand-alone product: this battery is a fully functional all-solid state thin film battery, that could provide the power needed for microdevices such as energy harvesting solutions. The employed materials are produced through scalable technologies for size/cost reduction, following a technological path towards the complexity of 3D thin film batteries, aimed to increase cell capacity for the same area footprint. The innovativeness is that these all-solid state microbatteries are based on an all-spinel configuration, providing high capacity and power. In addition, 3D thin film microbatteries are suitable for high-capacity/power demanding applications. Unique selling proposition: this technology is a unique concept of Si-compatible, 3D all-solid state thin film battery.
KER5 Expectations Table
Manufacturing, Realisation: imec
Assembly: imec
Research: IREC, imec
Consultancy, Training: CERR, imec
Utilisation in other business: CERR, imec
Saling, distribution: --
Services: IREC, imec
Social and economic implications of the SiNERGY’s results
To better understand the scenery in which SiNERGY innovation is taking place, and the prospects of impact in social and economic terms that its results can generate, a brief analysis of the impact of some technologies and devices and that can benefit of these results is thereby presented. In details, a short overview on EU IoT strategies and impact is presented, followed by a focus on the microelectromechanical systems (MEMS) and the envisaged socio-economic impact of two MEMS devices that can specifically take profit of SiNERGY research outcomes and enter more effectively in our everyday life.
As a premise, we should consider that what we call socio-economic impact is usually driven by business, and is a major predictor of business success. Companies affect people’s assets, opportunities, capabilities, and standards of living in many different ways. Thus companies are on their side conditioned by their customer’s approval. As a result, companies are increasingly interested in measuring the socio-economic impact of their products, that is, as in our case, in the introduction of novel technologies on the market.
IoT landscape in EU
The EU2020 strategy for growth, with target objectives, priorities and initiatives for a smart, sustainable and inclusive growth, has been clearly defined. Within this strategy, ICT plays a strong role.
The “Internet of Things” concept, indeed, intended as the ever-growing network of physical objects that communicate via IP between them and with other Internet-enabled devices and systems, is fully aligned with this vision, and is expected to be an essential cornerstone to this industrial revolution.
Economic impact: the “smart growth” driving force in the EU vision relies on the development of a strong knowledge economy, and the IoT development in Europe is expected to support this vision intensely. In this sense, the research through EU is already at the forefront of the development of many of the necessary components of an internet of things. The market expectations for the IoT in the next years are very high, and are strictly related to the society needs and expectations. This market, and the related predictions, is, by the way, very complex, being driven by a multifaceted ecosystem of different actors that play specific roles: research organization, as key provider of technologies; existing Industrials as provider of supporting infrastructures for the ecosystem; data providers; SMEs and Start-ups for production of end user applications; regulation authorities.
Societal and environmental impact: EU is fronting inequalities between different regions/states, as well as demographic (ageing population) and societal challenges (unemployment is a critical issue in certain areas). In addition to supporting a “smarter” and more sustainable society, the Internet of Things vision can also have a decisive impact on the inclusiveness of society by supporting not only a higher quality of life but also reducing inequities. This impact is more evident on health, security and, of course, economic issues. Environmental Impact is also key to EU 2020 agenda. In this direction, there is a strong expectation from the society on the future role of IoT to address sustainability issues, and in particular sustainable food, resources, energies, industries and services, transports.
Microelectromechanical Systems (MEMS) in IoT
Sensors and actuators are critical devices for transferring information between the physical and digital worlds. While early sensors were large, bulky, and prone to failure, advances in miniaturization have led to micro-scale devices that can be combined on a single chip. These MEMS are already revolutionizing medical care, automotive and industrial diagnostics, and are poised to lead to rapid advances in haptic control, as accelerometers and gyroscopes are placed in every electronic device a person carries. As smartphones replace entire laboratories of equipment, the $12 billion MEMS market is experiencing annual growth rates of more than 20%.
Over the last decade there has been a growing emphasis on adding embedded intelligence to the world around us in order to make it smarter. This vision of smart encompasses cities, transport, energy, health, homes, and public buildings, among other areas. The goal of smarter environments and activities is driven by the complex mixture of challenges outlined in this chapter. We increasingly need creative solutions that can do more with less to meet these growing challenges. Innovation should be about bringing a great idea to market: 60% of the world population will live in cities by 2020, creating enormous challenges in delivering sustainable living environments for those city dwellers.
Sensors are playing and will continue to play a key role in enabling innovative solutions. Smart technologies—such as smart sensors, data acquisition systems, ubiquitous data connectivity, and big data analytics—provide key technology building blocks. Integrated appropriately, they provide efficiencies, scalability, and cost reduction. They also act as an innovation platform for long-term solutions to enable meaningful citizen engagement or “stickiness.” The potential of these systems will continue to evolve, particularly as the trajectory and merging of technologies increases.
One of the main challenges for wireless sensor networks is how to power these sensor nodes. Use of wired power limits the viable locations (and ultimately numbers) of sensor nodes and may preclude gathering essential information. Batteries, on the other hand, need eventual replacement. This is an expensive (and, in some cases, impractical) proposition for networks with large numbers of nodes, some or all of which may be dif cult to access. Moreover, batteries are constrained to a limited temperature range.
SiNERGY objectives foresee to overcome limits and support low-power sensor nodes targeting 2 of the products that are recognized among the most challenging in the Internet of Things:
1. Tire Pressure Monitoring System.
2. Autonomous device in home and industrial appliances.
The aim of the Consortium is to provide MEMS energy harvesters that convert environment vibration or heat into electricity. Current MEMS technology is not capable to create and deliver enough energy to power up sensors. Energy Harvesting in Tires is considered one domain in the area of the disruptive technologies that is widely considered as the most challenging in the Internet of Things universe of advances as it requires breakthrough in mechanical engineer, RF design, energy efficiency, robustness at high stress up to 3000g, resistance to automotive temperature that range from -40 +125°C. It also requires breakthrough and innovation in wireless communication such as ultra-low energy consumption, high power output, high rate of RF link margin budget, high performances in RF propagation and resiliancy to effect such as Doppler, multipath radiowaves propagation and other particular tasks. Sensors in tires are by far considered the first example of Internet of Things that is already commercially available (due to regulatory frames in US and EU) and sold in volume.
Generally, breakthrough technology classification, as in standard off the shelf technology, complies to following criteria:
1. Technologies must have progressed beyond lab-scale validation and have Signs of Economic Success. On the other hand, such technologies will have already shown signs of successful commercialization and are beginning to enter the marketplace: Even the most breathtaking innovations have severely limited utility if they remain conned to the laboratory due to high costs or missing infrastructure.
2. Interdisciplinary Impact: disruptive technologies, such as the Internet of Things and Energy efficient wireless and autonomous sensors, impact multiple industries simultaneously, becoming global phenomena. They have the potential to transform several industries simultaneously and are not limited in scope to a particular domain such as autonomous wireless sensors in tires or in industrial appliances.
3. Near term Consequences. In few decades our world will barely resemble the world of today. Yet, it is almost impossible to predict exactly how that world will be different: they must be on the cusp of major breakthroughs and expected to have significant impacts in the next decade.
4. Revolutionary Potential. They must be radically revolutionary and likely to disrupt, rather than extend existing industries. Although these technologies build on existing developments, they are likely to trigger significant changes to business models and practices as they are implemented.
Cooking vessels socio-economic impact
Domestic and professional appliances are equipment that uses a lot of energy but, in some cases, a significant part is lost. A typical example is a gas burner that, when used to heat a pot, has an efficiency of 60%. That means that 40% of the energy is wasted (most of it in exhausted gases). But there are several other examples of wasted energy: in boilers, pipes for hot water or steam transport, infrared heaters, heat exchangers and others.
With the ever increasing attention to the environmental sustainability and to the need of doing things better and better, the opportunity of using waste is becoming a must.
In SiNERGY Project it has considered a gas powered fryer, where part of the heat dispersed in the exhausted gases is converted into electricity to supply an electronic board. It is well known that gas-powered appliances, like the fryer, have no electrical energy on board and that is a great limitation in terms of control and monitoring. In fact, in these cases, the process control (oil temperature), is done thorugh an electro-mechanical component (thermostat based on fluid-expansion) that, for its nature, is not so accurate and cannot be even monitored from kitchen control systems.
A precise control of oil temperature is important because it affects characteristics of food (both for sensorial aspects than for health). Frying at a too low temperature make final food with too fat. Frying at too high temperature make it too dried and singed. This last fact is even worse because of acrylamide. This chemical doesn’t appear to be in raw foods themselves. It’s formed when certain starchy foods are cooked at high temperatures for long periods of time.
The temperature measurement in Foodservice Industry is extremely important also for other reasons:
Food safety
Time and temperature are the two most important factors to control and monitor in the prevention of food borne illnesses.
Infectious diseases spread through food or beverages are a common, distressing, and sometimes life-threatening problem for millions of people around the world.
After a number of food crisis, the EU marked a shift to a more pro-active food policy and a new legislation. The HACCP (Hazard Analysis and Critical Control Points) system represents the key element for an early warning system at the production site and enables manufacturers to take preventive measures based on real data and hazard analysis. HACCP is nowadays a globally used safety philosophy to ensure the safety of foodstuffs. The monitoring and control of food temperature is a cornerstone in the management of HACCP, and no one can give up.
Quality and performances
Temperature is a parameter equally critical to obtain the desired quality of the cooking, not only for fried foods. If the importance of food temperature measurement cannot be questioned, the usefulness of having it wirelessly is equally well known. Wireless food-probes are very handy, wiring of the equipment is simplified, and connectivity with central control unit is also simplified.
The combination between «energy harvesting» and «wireless communication» is then of special interest of gas-powered appliances that represents an important business in all South Europe Market (because of the cost of electrical energy). In these cases, to have an “electronic like control” without having “electrical/electronic appliances” is a competitive advantage (no electrical plug, no electrical certification).
This is becoming particularly relevant now that, «Internet of Things» model is entering more and more in everyday life, with a growing number of products that must be connectable to their ecosystems. The most important recent exhibitions in the world, like IFA in Berlin and CES in Las Vegas, has clearly confirmed this trend.
New Consumers, and digital natives are among these, expect to have almost everything connected to their smartphones. There is a growing need to monitor everything from everywhere. Doing that for pure mechanical products is impossible and that creates a sort of discomfort.
Digitalization allows improving even those processes that have been up not so close. Cooking is among these and there is an increasing attention to it.
From the industrial point of view, the possibility of using a thermal harvester to power an electronic board is not a minor point. There is no need to have plugs, cables, power supply units nor batteries that could be the alternative solution. It is not necessary to certify the equipment to LVD (Low Voltage Directive). Also it is an advantage from the environmental point of view since useful work can be done with the energy already available.
Improved tire efficiency socio-economic impact
Use of vehicles in general showed that the working condition of tires, besides subjective driver behaviour, should be monitored by controlling the air pressure inside the tire: being the sole part of the vehicle that is in constant contact with the ground, the “tire contact patch area” it is important on constantly monitor its condition as a function of inflation rate. The correct positioning of the “tire contact patch area” significantly affects vehicle’s security, and contributes to Rolling Resistance rate of vehicle that can increase fuel consumption due to higher exhaust emissions. In addition, defective tires reduce vehicle performance, reduce braking and acceleration efficiency and reduce the efficiency of management and driving comfort.
It is therefore considered as a mandatory task to put considerable attention directed towards the control and management of the correctness of the tire condition by monitoring tire pressure and inflation as reported in the tire placard. An important element for controlling the tire pressure levels is the so called TPMS (Tire Pressure Monitoring Systems) devices that some countries ruled out as a mandate to install such system in vehicles with aim to improve safety and reduce pollution.
As a consequence of the directive of such system in the territory of the USA (NHTSA FMVSS138), in 2007 Bridgestone conducted extensive research in 19 EU countries. The results showed that as many as 38% cars used tires inappropriately inflated, contributing to increase danger in road traffic and CO2 emission because of a higher rolling resistance and consequent increase of friction and rate of dynamic.
Similar studies conducted in Europe clarified that approximately 90% of European motorists drive with at least one tyre underinflated and 12% drive cars with tyres in danger of failure. Tyre underinflation poses significant concerns on (i) safety in vehicles, since 9% of fatal accidents on motorways are related to tyre failures because of tire wear, and (ii) environment, as it contributes to the waste of billions of litres of fuel and around 10 MT excess in CO2 emissions. The recently adopted EU’s General Safety Regulation prescribes that ‘accurate’ systems should be fitted to new cars as of 2012 to increase safety and reduce CO2 emissions. The regulatory body UN-ECE, similarly to US mandate following to NHTSA FMVSS138 prescription, has recently required the mandatory use of TPMS in vehicles on the European territory.
Thus the widespread adoption of tire efficiency programs over the next decade will reduce vehicle fuel consumption by approximately 3%, and reduce global well-to-wheels greenhouse gas emissions by 100 million metric tons per year in 2020. This improvement would avoid the emission of more than 45,000 metric tons per year of nitrogen oxides and 10,000 metric tons per year of fine particulates from upstream fuel production and refining.
SiNERGY Dissemination activities
SiNERGY’s Consortium partners have been involved in wide dissemination activities, which mainly proceeded via website, conferences, international fairs, workshops and public speeches. A well-defined and structured set of dissemination activities has been carried out to foster awareness of SiNERGY main results in the society, scientific community and industry, thus facilitating the exploitation of Micro and Nano-powered sensors and smart system solutions in a wide range of application sectors.
Three SiNERGY main events have been organized, in conjunction with other relevant European initiatives to share and exchange ideas. Furthermore, as research turns in results, the relevant activity not subjected to IPR restriction has been made public available. All the activities have been recorded on the PUDF – Section A.
Attention has also been given to keep updated the SiNERGY website in its public area with news and other relevant information, while the private area has been enriched by reserved documents.
Scientific publications and generic information for common people, calendar to relevant international events, and general advertising have also been made publically available. Relevant scientific and technical results have been published in international journals mainly referring to sensors, electronics, microenergy, nanomaterials and MEMS technology, in such a way reaching all the main target groups identified in the dissemination and exploitation strategy. Similarly, a project presentation, project poster, project leaflet, two newsletters and two videos (a 2” short one - https://www.youtube.com/watch?v=lOwmP6n4G1s and a 11” extended one - https://www.youtube.com/watch?v=dADrj1W3Eis) have been produced.
The analysis of PUDF-A, devoted to track dissemination activities, shows the following main results with a very good overlap with the target groups identified in deliverables D6.2:
✓ 90 dissemination events in total (among which 48 conferences & workshops, 16 presentations/posters/other and several videoclips)
✓ > 7200 people involved in the events;
✓ 8 press articles published
✓ Close to 30 peer reviewed scientific publications / book chapters
All partners were involved in the dissemination according to their roles and results achieved, contributing to the presentations delivered by the project coordinator and WP leaders/deputies thus actively participating in UE working groups, EU sponsored events and Technological Platforms for project visibility.
The SiNERGY website has been periodically monitored by Google Analytics to gain further insight in terms of communication efficiency and functionality, further optimized in Search Engine Optimization context. To date, the analysis discloses worldwide connections with constantly rising shares from new connections as result of dissemination events carried out by SiNERGY partners and the Search Engine Optimization activities.
The three main dissemination events mentioned before are:
• SiNERGY 1st workshop, as a part of the LET’S 2014 international conference held under the Italian presidency of the EU, which dealt with the role of Key Enabling Technologies – Bologna, 29th Sep - 1st Oct 2016
• SiNERGY 2nd Workshop, inside the Energy Harvesting Systems – “FlexTEG” - June 25-26, 2015 @ Fraunhofer IWS Dresden
• E-MRS SIMPOSIUM W [Materials and systems for micro-energy harvesting and storage]- held in the general frame of the E-MRS Spring meeting (2-6 May 2016) in Lille (France)
They were organized according to the spirit of the planned activities in the DoW. For the later, it was decided that opting for an open symposium rather than a closed workshop was worth trying from the point of view of a broader dissemination of SiNERGY goals and general micro-energy issues and that was the case.
So far it is worth mentioning that, in addition to SiNERGY (GA nº604169), the symposium counted with the help and support of other EU funded storage and harvesting projects such as NanoCaTe (GA nº604647), MATFLEXEND (GA nº604093) and MANpower (GA nº604360), which provided both members for the scientific committee and some proposals for invited speakers. This was also the case for the second SiNERGY workshop, which was sponsored by the NanoCaTe project.
To their own extent, the three SiNERGY events have offered a wide and international platform for discussion on energy harvesting materials, storage materials, integrated systems for energy harvesting and storage, applications and business scenario.
As an aftermath of these four European projects joining their forces, a common presentation of their works in the field of energy harvesting and storage was accepted in the Industrial Technologies event held June 22-24 in Amsterdam under the Dutch presidency of the EU. On such occasion, SiNERGY had the opportunity of advocating for the microenergy topic presenting the complementary approached of the four projects. This role also extended to the participation in a concurrent meeting of the Advanced Materials and Nanotechnologies for Energy Applications Cluster, which portrays an initial orientation biased towards macroenergy applications. In this respect, SiNERGY stressed the intrinsic and practical interests of microenergy regarding both materials and nanotechnologies and pointed to the fact that in our case nanotechnologies are not only a mean to improve materials as mostly done by macroenergy approaches but also to fabricate the microenergy devices themselves.
List of Websites:
sinergy-project.eu
