Periodic Reporting for period 4 - MEMS 4.0 (Additive Micro-Manufacturing for Plastic Micro-flectro-Mechanical-Systems)
Reporting period: 2022-04-01 to 2023-05-31
Micro-Electro-Mechanical-Systems (MEMS) rely on solid-state materials benefiting from the semiconducting and mechanical properties. Today, a shift towards flexible substrates and biocompatible materials occurs, driven by demand for wearable and implantable devices. New manufacturing techniques are needed that go beyond today’s capabilities. A coordinated approach is undertaken in this project to push forward key techniques and to integrate them into reliable platform.
The project is by setting a focus on additive methods at micro- and nanoscale, self-assembly and local thermal processing. We are targeting biocompatible and implantable MEMS as well as low dimensional materials, because these MEMS are most challenging to fabricate, but if successful, they also have an enormous impact for future applications.
Following techniques have been explored throughout the entire project.
Stencilling is a lithography-free direct additive manufacturing technique for material structures made entirely in vacuum. It enables clean 2D and 2.5D patterns at micro and nanoscale, is rapid and cost-efficient, and scalable to large substrates, also on biodegradable materials. By introducing so-called 'bridge-stencils', we overcame a major limitation of stenciling, namely the design freedom validated by a RLC device directly integrated on a biodegradable polymer substrate.
Drop-on-demand inkjet printing focused specifically on mix-and-match fabrication related to biocompatible and biodegradable plastic MEMS. We implemented a dual-ink printing approach, where the second ink seals the first ink inside a microcontainer to protect it from evaporation.
Bottom up capillary-assisted particle assembly (CAPA) are candidate for plastic MEMS because no harsh lithography processes are needed. We demonstrate here that the technique can be upscaled by a reproducible repetitive assembly/transfer.
We discovered a truly original and unique way to use a thermal scanning probe lithography (t-SPL) to directly cut 2D materials with the local heat, and further to engineer strain into the 2D material by creating surface waves.
The project results enable completely new ways to shape functional, biocompatible and biodegradable MEMS. It builds up deeper understanding on materials processing and device integration and forms a guide to develop future MEMS manufacturing tools and methods. The reduction of materials and fabrication costs by digital AM allows for a more favorable ecological footprint of future manufacturing.
The project is by setting a focus on additive methods at micro- and nanoscale, self-assembly and local thermal processing. We are targeting biocompatible and implantable MEMS as well as low dimensional materials, because these MEMS are most challenging to fabricate, but if successful, they also have an enormous impact for future applications.
Following techniques have been explored throughout the entire project.
Stencilling is a lithography-free direct additive manufacturing technique for material structures made entirely in vacuum. It enables clean 2D and 2.5D patterns at micro and nanoscale, is rapid and cost-efficient, and scalable to large substrates, also on biodegradable materials. By introducing so-called 'bridge-stencils', we overcame a major limitation of stenciling, namely the design freedom validated by a RLC device directly integrated on a biodegradable polymer substrate.
Drop-on-demand inkjet printing focused specifically on mix-and-match fabrication related to biocompatible and biodegradable plastic MEMS. We implemented a dual-ink printing approach, where the second ink seals the first ink inside a microcontainer to protect it from evaporation.
Bottom up capillary-assisted particle assembly (CAPA) are candidate for plastic MEMS because no harsh lithography processes are needed. We demonstrate here that the technique can be upscaled by a reproducible repetitive assembly/transfer.
We discovered a truly original and unique way to use a thermal scanning probe lithography (t-SPL) to directly cut 2D materials with the local heat, and further to engineer strain into the 2D material by creating surface waves.
The project results enable completely new ways to shape functional, biocompatible and biodegradable MEMS. It builds up deeper understanding on materials processing and device integration and forms a guide to develop future MEMS manufacturing tools and methods. The reduction of materials and fabrication costs by digital AM allows for a more favorable ecological footprint of future manufacturing.
1. Stenciling:
Microstencils were first fabricated by photolithography and later by DUV lithography. Metallic micro/nanostructures were stenciled onto biocompatible stretchable materials leading to the discovery of an original method to create large-scale liquid metal structures. To overcome the issue of design topology limitations, we implemented successfully so-called bridge-stencils and exploited the blurring effect, that allow for arbitrary shapes to be stenciled [Sun et al. Advanced Materials Technologies (2023)].
2. Printing
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). Printing was further perfected and used throughout the project to deliver improved print results of functional inks, such as drug solutions [Park et al. Advanced Functional Materials (2023)].
3. Self-assembly
A scalable transfer technique has been demonstrated to use templated capillary self-assembled nanoparticles and rods as functional devices. As demonstrator an electron-tunneling based strain sensor was developed. The sensor is built on a stretchable biocompatible substrate poly(dimethylsiloxane) (PDMS), useful for wearable or implantable devices. Yield studies to upscale the method have been performed [HSC Yu, et al. Particle & Particle Systems Characterization (2022)] and showed also, that this approach is not yet mature for being considered for reliable nano-manufacturing.
4. Thermal nanoprocessing
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 [Liu et al. Adv. Mater. 2020]. A comprehensive thermal nano-processing library was published as an open-access review article. [Howell et al. Microsys. Nanoeng. 2020, 6]. Finally, we have succeeded in developing a new pattern transfer method from thermal resist into dielectrics [Erbas et al. ChemRxiv, 2023].
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 a new imprinting process. [M. Rüegg PhD Thesis EPFL 2020] The 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. [Rüegg et al. Adv. Fun. Mater 2019, 29 (39)] The work has been reported in scientific journals and also presented as invited paper [J Park, J Brugger, 2022 International Electron Devices Meeting (IEDM), San Francisco, USA]
6. Implantable permanent MEMS
Here we focused our work on glassy carbon microsensors and demonstrated a device by using the pyrolized SU-8 integrated in a SU-8 cantilever as strain sensor. The original results are reported in a paper [J Jang, G Panusa, G Boero, J Brugger Microsystems & Nanoengineering 8 (1), 22 (2022)]. The paper shows that the glassy carbon behaves like a metallic strain gage without extraordinary piezo-resistive effect.
Microstencils were first fabricated by photolithography and later by DUV lithography. Metallic micro/nanostructures were stenciled onto biocompatible stretchable materials leading to the discovery of an original method to create large-scale liquid metal structures. To overcome the issue of design topology limitations, we implemented successfully so-called bridge-stencils and exploited the blurring effect, that allow for arbitrary shapes to be stenciled [Sun et al. Advanced Materials Technologies (2023)].
2. Printing
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). Printing was further perfected and used throughout the project to deliver improved print results of functional inks, such as drug solutions [Park et al. Advanced Functional Materials (2023)].
3. Self-assembly
A scalable transfer technique has been demonstrated to use templated capillary self-assembled nanoparticles and rods as functional devices. As demonstrator an electron-tunneling based strain sensor was developed. The sensor is built on a stretchable biocompatible substrate poly(dimethylsiloxane) (PDMS), useful for wearable or implantable devices. Yield studies to upscale the method have been performed [HSC Yu, et al. Particle & Particle Systems Characterization (2022)] and showed also, that this approach is not yet mature for being considered for reliable nano-manufacturing.
4. Thermal nanoprocessing
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 [Liu et al. Adv. Mater. 2020]. A comprehensive thermal nano-processing library was published as an open-access review article. [Howell et al. Microsys. Nanoeng. 2020, 6]. Finally, we have succeeded in developing a new pattern transfer method from thermal resist into dielectrics [Erbas et al. ChemRxiv, 2023].
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 a new imprinting process. [M. Rüegg PhD Thesis EPFL 2020] The 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. [Rüegg et al. Adv. Fun. Mater 2019, 29 (39)] The work has been reported in scientific journals and also presented as invited paper [J Park, J Brugger, 2022 International Electron Devices Meeting (IEDM), San Francisco, USA]
6. Implantable permanent MEMS
Here we focused our work on glassy carbon microsensors and demonstrated a device by using the pyrolized SU-8 integrated in a SU-8 cantilever as strain sensor. The original results are reported in a paper [J Jang, G Panusa, G Boero, J Brugger Microsystems & Nanoengineering 8 (1), 22 (2022)]. The paper shows that the glassy carbon behaves like a metallic strain gage without extraordinary piezo-resistive effect.
During the research thermal nanoprocessing we discovered as innovative fabrication process to create sub-20 nm structures of 2D materials. Our work on t-SPL related to strain engineering of 2D materials using deterministic surface topographies has delivered new data for 2D electronics that show very promising electron mobility tuning. This work is currently being wrapped up and several papers with reference to the project are in submission phase.
An important progress beyond the state of the art has been achieved in the field of implantable biodegradable MEMS, where the MEMS 4.0 team was able to develop a versatile technology for wirelessly controlled drug release using biodegradable materials. Filling microcapsules with precise amounts of functional inks (e.g. drugs) and corresponding encapsulation was known to be a major challenge. We are very proud to have solved this challenge by a highly-precise dual-printing approach, that has proven its effectiveness for our concrete case study, but that is generic and can be applied to a variety of other materials dispensing challenges.
During the entire project all technologies addressed made 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. As such, the results from the project enable novel polymer-based MEMS technologies to be implemented together with the standard processing methods that are already established.
An important progress beyond the state of the art has been achieved in the field of implantable biodegradable MEMS, where the MEMS 4.0 team was able to develop a versatile technology for wirelessly controlled drug release using biodegradable materials. Filling microcapsules with precise amounts of functional inks (e.g. drugs) and corresponding encapsulation was known to be a major challenge. We are very proud to have solved this challenge by a highly-precise dual-printing approach, that has proven its effectiveness for our concrete case study, but that is generic and can be applied to a variety of other materials dispensing challenges.
During the entire project all technologies addressed made 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. As such, the results from the project enable novel polymer-based MEMS technologies to be implemented together with the standard processing methods that are already established.