Post-Release Metallization in MEMS Silicon-to-Silicon Contact Switches for On-Resistance Improvement

TL;DR

This paper introduces a new method to improve the performance of MEMS switches by adding metal coatings after fabrication, reducing contact resistance and increasing reliability.

Contribution

The study presents a post-release metallization technique using Pt and Al/Cr to enhance the on-resistance of MEMS silicon-to-silicon contact switches.

Findings

Platinum coatings achieved a contact resistance of 406 Ω at 1 mA.

Aluminum over chromium showed reduced resistance at higher currents, possibly due to oxidation.

Metallization improved surface and edge coverage, enhancing switch repeatability.

Abstract

This work reports a post-release sputter-metallization process for microelectromechanical systems (MEMS) switches with silicon-to-silicon (Si-to-Si) contacts fabricated by deep reactive ion etching. Platinum (Pt) was selectively deposited on the contacting platforms through a perforated mask. Alternatively, aluminum (Al) was deposited over a thin chromium (Cr) adhesion layer. Electrical measurements showed that Pt enabled a contact resistance on the order of 406 Ω at a 1 mA test current, whereas the resistance of Al/Cr coatings decreased from 7.94 kΩ at 1 mA to 270 Ω at 25 mA, a change that was potentially linked to oxidation of the Al. These results demonstrated successful coating, with uniform top-surface and edge coverage as revealed by energy-dispersive X-ray spectroscopy imaging. Overall, the results indicate that post-release metallization has the potential to improve the operational repeatability of Si-to-Si contact MEMS switches in static and dynamic tests; the findings also point to process refinements to further optimize contact resistance.

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