Additive Micromanufacturing: Multimetal Multiphase Functional Architectures

Project Information

AMMicro

Grant agreement ID: 101078619

DOI

10.3030/101078619

EC signature date 22 November 2022

Start date 1 April 2023

End date 31 March 2028

Funded under

• European Research Council (ERC)

Total cost

€ 1 498 356,00

EU contribution

€ 1 498 356,00

Coordinated by

MAX-PLANCK-INSTITUT FUR NACHHALTIGE MATERIALIEN GMBH
Germany

Periodic Reporting for period 1 - AMMicro (Additive Micromanufacturing: Multimetal Multiphase Functional Architectures)

Reporting period: 2023-04-01 to 2025-09-30

Summary of the context and overall objectives of the project

Microfabrication technologies are vital to the miniaturization of engineering components for applications in energy harvesting, electronic devices, and microelectromechanical systems (MEMS). One of the most promising emerging microfabrication techniques is localized electrodeposition in liquid (LEL), which is capable of freeform printing 3D metal microarchitectures and has the potential to transform research fields such as micro-/nanomechanics, microelectronics, MEMS fabrication and packaging, phononics, photonics, and catalysis. The aim of the Additive micromanufacturing (AMMicro) project is to fabricate advanced multimaterial/multiphase MEMS devices with superior impact-resistance and self-damage sensing mechanisms.

LEL combines electrochemical reduction with a highly sensitive force-sensing scheme, allowing real-time monitoring of the growth of each metal voxel (Exaddon AG). The local metal ions supplied from the hollow AFM tip confines the electrochemical reduction to the substrate. The optical laser beam deflection system detects the completion of voxel deposition at the current location and moves the tip to the next deposition location. Therefore, LEL technique enables the printing of 3D metal microarchitectures with complex arbitrary shapes in a voxel-by-voxel layer-by-layer fashion. We are able to print different 3D metal microarchitectures using the LEL technique, including micropillars, microlattices, microtensile bars, and microcantilevers.

The LEL method for micro-scale additive manufacturing operates in a liquid environment crucial for the electrodeposition process. This technique enables the precise fabrication of complex metallic microstructures and uniquely facilitates the encapsulation of liquids within these 3D metal structures. Utilizing precise printing methods, it is possible to encapsulate even pico-liter volumes of liquid in a single step. This capability allows the creation of liquid-encapsulated 3D microstructures, where the liquid can influence the mechanical response of the structure. Our research focuses on investigating the impact of encapsulated liquid on the mechanical properties of metal-liquid microstructures and their interactions. We will conduct mechanical tests under various temperatures, strain rates, and vibrational conditions to systematically study these effects. Furthermore, this unique architecture allows for the study of ice properties and the potential to encapsulate other materials along with the liquid, expanding the scope of applications. Also, the AMMicro project aims to fabricate 3D metal MEMS-based mechanical testing devices consisting of actuating and sensing features that can be combined with microscopy techniques to test nanomaterials at the micro- and nanoscale.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To evaluate the mechanical properties of copper structures fabricated via the localized electrodeposition in liquid (LEL) method, we investigated the mechanical properties of copper structures fabricated via the LEL method through uniaxial compression tests on micro-pillars and lattice structures. The results revealed distinct strain rate- and temperature-dependent behavior. Building on our understanding of the mechanical response of these simple copper structures, we evaluated their mechanical behavior in more complex geometries, including honeycombs and octet microlattices under application relevant extreme strain rates and temperatures. The results show excellent specific energy absorption properties and demonstrate the possibility and the potential of applying micro-honeycomb architectures as impact protection architectures for sensitive micro/nano-electromechanical systems at extreme loading conditions.

For LEL-based 3D printing, the applied potential controls the overpotential during electrodeposition, allowing tuning of the grain size and overall microstructure of the printed architecture. Our research demonstrates that within the potential range for copper printing, three different types of microstructure can be achieved. By applying different overpotentials, we achieved microcrystalline, ultrafine-grained, and even mixed microstructures.

Since the LEL method is based on electrodeposition, the entire printing process must be carried out in a submerged liquid environment. This enables the fabrication of unique liquid-metal multiphase microarchitectures by printing hollow metal vessels with encapsulated liquid inside. These structures were successfully printed, and their mechanical properties were evaluated across various temperatures and strain rates.

Also, we developed a novel micro-scale (µ-) fixture for micro/nanomechanical testing, enabling a wide range of micromechanical tests such as tension, shear, fracture, and fatigue. The fixture design was optimized through FEM simulations for both geometry and mechanical response. Its flexibility and structural robustness mark a significant advancement in 3D-printed micro/nanomechanical testing platforms.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The properties of metal microarchitectures are determined by both geometry and microstructure. The focus has been on optimizing the geometry to achieve better properties. The LEL-based 3D printing has enabled the fabrication of metallic microarchitectures. By controlling the printing parameter potential, the microstructure can now be tuned for the first time. With different microstructures, the properties of the microarchitectures can also be tailored. With the combination of the geometry and microstructure design, we would be able to manufacture micro-architectures with improved properties.

Liquid-encapsulated microarchitectures represent a highly unique and promising feature. While there have been previous attempts to encapsulate liquid within metallic shell structures, these approaches have been largely limited by fabrication constraints. Using the LEL-based printing method, we have successfully fabricated liquid-encapsulated structures at the microscale with precise control over picoliter-scale liquid volumes. This platform opens new opportunities for studying the properties of ice, as the robust metal shell can prevent water evaporation and allow freezing even under vacuum conditions. It also provides a feasible route for investigating chemical reactions in extremely small liquid volumes and for encapsulating micro/nanoparticles within the liquid cavity of the structure, for novel sample preparation techniques for Cryo-TEM or APT.

The current state-of-the-art quantitative micromechanical testing can be conducted at testing speeds typically less than 1mm/s. Using piezo tube actuators and piezoelectric/piezoresistive load sensors, we have now extended the testing speeds to 100mm/s. We have also developed testing setups that can further combine these extreme strain rates with cryogenic temperatures upto 100K.

Another key recent development involved leveraging the LEL-based 3D printing method to fabricate µ-fixtures for micromechanical testing. We developed a novel 3D-printed microfixture design, with a key advantage of flexibility: fixture designs can be easily modified on the fly to accommodate different testing configurations or tailor the stiffness to suit materials with varying mechanical properties. This adaptability, combined with the robust structural performance of the printed fixtures, presents a significant advancement in micromechanical testing methodologies.

Liquid encapsulated copper microcylinders