MEMS micro-coils for magnetic neurostimulation
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Micro-coil magnetic stimulation of brain tissue presents new challenges for MEMS micro-coil probe fabrication. The main challenges are threefold; (i) low coil resistance for high power efficiency, (ii) low leak current from the probe into the in vitro experimental set-up, (iii) adaptive MEMS process technology because of the dynamic research area, which requires agile design changes. Taking on these challenges, we present a MEMS fabrication process that has three main features; (i) multilayer resist lift-off process to pattern up to 1800-nm-thick metal films, and special care is taken to obtain high conductivity thin-films by physical vapor deposition, and (ii) all micro-coil Al wires are encapsulated in at least 200 nm of ALD alumina and 6-μm-thick parylene C such the leak resistance is high (>210 GΩ), (iii) combining a multi-step DRIE process and maskless photolithography for adaptive design and device fabrication. The entire process requires four lithography steps. Because we avoided SOI wafers and lithography mask fabrication, the design-to-device time is shortened significantly. The resulting probes are 4-mm-long, 60-μm-thick, and down to 150 μm-wide. Selected MEMS coil devices were validated in vivo using mice and compared to previous work.
|Tidsskrift||Biosensors and Bioelectronics|
|Status||Udgivet - 2023|
The work presented in this article is supported by the Lundbeck Foundation , grant R305-2018-2779 , and the Novo Nordisk Foundation , grant NNF0064289 . AH acknowledges the support from the Marie and B. Richters Foundation . This work was sponsored by the NIH NEI R01-EY029022 (to SWL) and by the BRAIN Initiative NINDS U01-NS099700 and the Dept. of Defense/CDMRP ( VR170089 ) (to SIF). We thank Dr. Yubing Zhang for microCT measurements.
© 2023 The Authors