Periodic Reporting for period 3 - MEMS 4.0 (Additive Micro-Manufacturing for Plastic Micro-flectro-Mechanical-Systems)
Reporting period: 2020-10-01 to 2022-03-31
Micro-Electro-Mechanical-Systems (MEMS) are highly miniaturized systems composed of integrated circuits, sensors and actuators. Examples of such MEMS devices are accelerometers, gyroscopes, microphones, pressure and magnetic field sensors, which are often integrated into automotive and consumer electronics. The first generations of MEMS mainly relied on solid-state materials (Silicon and III-V semiconductors) benefiting from the semiconducting and micro-mechanical material properties. Today, a shift towards flexible substrates and biocompatible materials is taking place, driven by demand for wearable and implantable devices. For addressing the needs of these types of MEMS applications dedicated manufacturing techniques are needed that go beyond what is established today. A coordinated approach is needed to push forward some key techniques and to integrate them into reliable systems.
The MEMS 4.0 project is pushing the frontiers in new MEMS materials and new MEMS processing by setting a focus on additive methods at the micro- and nanoscale, self-assembly and local thermal processing. These techniques have large potential to successfully overcome fabrication challenges for next generation plastic MEMS. We are targeting biocompatible and implantable MEMS as well as functional devices from low dimensional materials, because these types of MEMS are the most challenging to fabricate, but if successful, they also have an enormous impact for future biomedical applications and flexible electronics.
The following fabrication techniques are going to be used, further developed and combined to form the new toolbox for advanced MEMS.
Stencilling: Stencilling is a lithography-free direct additive manufacturing technique for resist-free deposition material structures made entirely in vacuum. It enables ultra-clean 2D and 3D patterns at micro and nanoscale. It is rapid and cost-efficient, and scalable to large substrates. Here we aim to develop new stencil lithography methods as additive micro manufacturing tools to be used with and on biodegradable materials.
Printing: Drop-on-demand inkjet printing is established for a variety of material systems, including bio-inks. Here we will further develop this low-waste and rapid-prototyping method by addressing specifically mix-and-match issues related to biocompatible and biodegradable plastic MEMS.
Self-assembly: Bottom up techniques such as capillary-assisted particle assembly (CAPA) are intriguing for plastic MEMS because no harsh lithography processes are needed. We aim here concretely to build a toolbox for the self-assembly of fragile, ultra-small components and integrate them into plastic MEMS, aimed for wearables and implantables.
Thermal nanoprocessing: We will perform exploratory fundamental studies on how materials can be processed with heat at the micro and nanoscale. We will use thermal scanning probe lithography (t-SPL) to locally modify material properties that can be useful for strain sensors for wearables and implantables.
The objective of MEMS 4.0 is to move from the existing MEMS toolbox into the area of biocompatible and biodegradable polymer MEMS solutions. As a framework for the process engineering, the results of MEMS 4.0 will enable new generations of miniaturized micro/nano(bio)systems to be developed and manufactured for future applications, primarily for wearables and implantables. Most importantly, this will provide completely new ways to design and (3D) shape functional, biocompatible and biodegradable, materials. It will allow generally a much deeper understanding on the materials processing and device integration, and will form a guide to design and develop for the future MEMS manufacturing tools and methods. Last but not least, the reduction of materials and fabrication costs by making use of digital AM schemes allows for a major reduction of the ecological footprint of future manufacturing, which is a very important potential benefit of the MEMS 4.0 project.
The MEMS 4.0 project is pushing the frontiers in new MEMS materials and new MEMS processing by setting a focus on additive methods at the micro- and nanoscale, self-assembly and local thermal processing. These techniques have large potential to successfully overcome fabrication challenges for next generation plastic MEMS. We are targeting biocompatible and implantable MEMS as well as functional devices from low dimensional materials, because these types of MEMS are the most challenging to fabricate, but if successful, they also have an enormous impact for future biomedical applications and flexible electronics.
The following fabrication techniques are going to be used, further developed and combined to form the new toolbox for advanced MEMS.
Stencilling: Stencilling is a lithography-free direct additive manufacturing technique for resist-free deposition material structures made entirely in vacuum. It enables ultra-clean 2D and 3D patterns at micro and nanoscale. It is rapid and cost-efficient, and scalable to large substrates. Here we aim to develop new stencil lithography methods as additive micro manufacturing tools to be used with and on biodegradable materials.
Printing: Drop-on-demand inkjet printing is established for a variety of material systems, including bio-inks. Here we will further develop this low-waste and rapid-prototyping method by addressing specifically mix-and-match issues related to biocompatible and biodegradable plastic MEMS.
Self-assembly: Bottom up techniques such as capillary-assisted particle assembly (CAPA) are intriguing for plastic MEMS because no harsh lithography processes are needed. We aim here concretely to build a toolbox for the self-assembly of fragile, ultra-small components and integrate them into plastic MEMS, aimed for wearables and implantables.
Thermal nanoprocessing: We will perform exploratory fundamental studies on how materials can be processed with heat at the micro and nanoscale. We will use thermal scanning probe lithography (t-SPL) to locally modify material properties that can be useful for strain sensors for wearables and implantables.
The objective of MEMS 4.0 is to move from the existing MEMS toolbox into the area of biocompatible and biodegradable polymer MEMS solutions. As a framework for the process engineering, the results of MEMS 4.0 will enable new generations of miniaturized micro/nano(bio)systems to be developed and manufactured for future applications, primarily for wearables and implantables. Most importantly, this will provide completely new ways to design and (3D) shape functional, biocompatible and biodegradable, materials. It will allow generally a much deeper understanding on the materials processing and device integration, and will form a guide to design and develop for the future MEMS manufacturing tools and methods. Last but not least, the reduction of materials and fabrication costs by making use of digital AM schemes allows for a major reduction of the ecological footprint of future manufacturing, which is a very important potential benefit of the MEMS 4.0 project.
Progress has been achieved on different fronts of the project:
1. Stenciling:
Microstencils have been fabricated by photolithography and deep UV (DUV) lithography and benchmarked for various application purposes including for usage on biocompatible substrates. Metallic micro/nanostructures were stenciled onto biocompatible stretchable materials leading to the discovery of an original method to create large-scale liquid metal structures on stretchable biocompatible substrates. These liquid metal structures are investigated as versatile strain gauges for polymeric MEMS.
2. Printing
One of the challenges in drug delivery systems is to encapsulate the active substance in order to protect it from deterioration. We have developed an innovative approach for encapsulation of liquid drugs in a biocompatible micro-container to prevent evaporation of the liquid media (i.e. water). The encapsulation media and the drug are sequentially inkjet printed into a reusable template, followed by UV curing of the encapsulation layer.
3. Self-assembly
An electron-tunneling based strain sensor has been developed. The sensor has the following three characteristics: i) it is built on a stretchable biocompatible substrate poly(dimethylsiloxane) (PDMS), which makes it useful for wearable or implantable devices, ii) the strain-sensitive electrical signal is measured through two self-assembled gold nanorods separated by a distance of less than 2 nm, iii) a slick device design transforms the macroscopic strain of the PDMS into a sub-Ångström displacement that can be detected through a change in the electron-tunneling current. [Yu et al. TRANSDUCERS & EUROSENSORS XXXIII 2019]
4. Thermal nanoprocessing
Thermal nanoprocessing of sub-100-nm structures through t-SPL is an emerging digital manufacturing technique. We have explored different ways to directly modify materials with a heated tip i.e. by annealing, melting or chemical modification. It was found that direct manipulation of 2D materials is an extremely compelling and versatile application of t-SPL. We have used t-SPL to locally cut 2D materials such as MoS2 or MoTe2 into arbitrary shapes [Liu et al. Adv. Mater. 2020, (accepted)]. A comprehensive thermal nano-processing library was published as an open-access review article. [Howell et al. Microsys. Nanoeng. 2020, 6]
5. Implantable biodegradable MEMS
We fabricated implantable biodegradable capsules for wireless controlled drug release made from biodegradable elastomers poly(glycerol sebacate) (PGS) and poly(octamethylene maleate (anhydride) citrate) (POMaC) by an innovative imprinting process. [M. Rüegg PhD Thesis EPFL 2020] The 10x10x20mm3-sized drug containers accommodate up to six isolated reservoirs to be loaded separately with a drug. The capsules were covered with thin membranes equipped with wirelessly powered magnesium microheaters that can be each addressed individually to release mL volumes of liquid drugs in each compartment separately. [Rüegg et al. Adv. Fun. Mater 2019, 29 (39), M. Rüegg PhD Thesis EPFL 2020] Wirelessly triggered release of the drug by breaking the membrane through heating was demonstrated, posing a significant step towards power receivers and microheaters for a variety of biodegradable implantable medical devices. [M. Rüegg PhD Thesis EPFL 2020]
1. Stenciling:
Microstencils have been fabricated by photolithography and deep UV (DUV) lithography and benchmarked for various application purposes including for usage on biocompatible substrates. Metallic micro/nanostructures were stenciled onto biocompatible stretchable materials leading to the discovery of an original method to create large-scale liquid metal structures on stretchable biocompatible substrates. These liquid metal structures are investigated as versatile strain gauges for polymeric MEMS.
2. Printing
One of the challenges in drug delivery systems is to encapsulate the active substance in order to protect it from deterioration. We have developed an innovative approach for encapsulation of liquid drugs in a biocompatible micro-container to prevent evaporation of the liquid media (i.e. water). The encapsulation media and the drug are sequentially inkjet printed into a reusable template, followed by UV curing of the encapsulation layer.
3. Self-assembly
An electron-tunneling based strain sensor has been developed. The sensor has the following three characteristics: i) it is built on a stretchable biocompatible substrate poly(dimethylsiloxane) (PDMS), which makes it useful for wearable or implantable devices, ii) the strain-sensitive electrical signal is measured through two self-assembled gold nanorods separated by a distance of less than 2 nm, iii) a slick device design transforms the macroscopic strain of the PDMS into a sub-Ångström displacement that can be detected through a change in the electron-tunneling current. [Yu et al. TRANSDUCERS & EUROSENSORS XXXIII 2019]
4. Thermal nanoprocessing
Thermal nanoprocessing of sub-100-nm structures through t-SPL is an emerging digital manufacturing technique. We have explored different ways to directly modify materials with a heated tip i.e. by annealing, melting or chemical modification. It was found that direct manipulation of 2D materials is an extremely compelling and versatile application of t-SPL. We have used t-SPL to locally cut 2D materials such as MoS2 or MoTe2 into arbitrary shapes [Liu et al. Adv. Mater. 2020, (accepted)]. A comprehensive thermal nano-processing library was published as an open-access review article. [Howell et al. Microsys. Nanoeng. 2020, 6]
5. Implantable biodegradable MEMS
We fabricated implantable biodegradable capsules for wireless controlled drug release made from biodegradable elastomers poly(glycerol sebacate) (PGS) and poly(octamethylene maleate (anhydride) citrate) (POMaC) by an innovative imprinting process. [M. Rüegg PhD Thesis EPFL 2020] The 10x10x20mm3-sized drug containers accommodate up to six isolated reservoirs to be loaded separately with a drug. The capsules were covered with thin membranes equipped with wirelessly powered magnesium microheaters that can be each addressed individually to release mL volumes of liquid drugs in each compartment separately. [Rüegg et al. Adv. Fun. Mater 2019, 29 (39), M. Rüegg PhD Thesis EPFL 2020] Wirelessly triggered release of the drug by breaking the membrane through heating was demonstrated, posing a significant step towards power receivers and microheaters for a variety of biodegradable implantable medical devices. [M. Rüegg PhD Thesis EPFL 2020]
Progress beyond the state of the art was mainly achieved along following research lines:
During the research thermal nanoprocessing we discovered an innovative fabrication process to create sub-20 nm structures of 2D materials and characterize them. An extensive process library for thermal nanofabrication with t-SPL has been created. We expect to extend the process library further and fabricate functional devices from the technology developed, and disseminate it to the community.
An important progress beyond the state of the art has been achieved in the field of implantable biodegradable MEMS, where the team was able to develop a versatile technology for wirelessly controlled drug release using biodegradable materials.
Until the end of the project we expect in all technologies addressed in this project significant advances by optimizing each of the fabrication techniques, to use them to fabricate functional devices and to combine them into a comprehensive process workflow and toolbox for soft-matter MEMS manufacturing.
During the research thermal nanoprocessing we discovered an innovative fabrication process to create sub-20 nm structures of 2D materials and characterize them. An extensive process library for thermal nanofabrication with t-SPL has been created. We expect to extend the process library further and fabricate functional devices from the technology developed, and disseminate it to the community.
An important progress beyond the state of the art has been achieved in the field of implantable biodegradable MEMS, where the team was able to develop a versatile technology for wirelessly controlled drug release using biodegradable materials.
Until the end of the project we expect in all technologies addressed in this project significant advances by optimizing each of the fabrication techniques, to use them to fabricate functional devices and to combine them into a comprehensive process workflow and toolbox for soft-matter MEMS manufacturing.