A CMOS-MEMS mirror with curled-hinge comb drives

TLDR

The device enables applications in biomedical imaging, optical switching, scanning, interferometry, and gyroscopes. The mirror is fabricated by integrating CMOS interconnect layers with a thick silicon substrate, using a slight silicon undercut etch for isolation, coating a 40 µm single‑crystal silicon plate with aluminum, and performing conventional CMOS processing followed by dry‑etch micromachining. The mirror achieves ±4.7° angular displacement at 18 Vdc, exhibits only 0.5 µm peak‑to‑peak curling, and eliminates the need for wafer bonding or precise front‑to‑backside alignment.

Abstract

A micromirror achieves up to ±4.7° angular displacement with 18 Vdc by a comb-drive design that uses vertical angled offset of the comb fingers. Structures are made from a combination of CMOS interconnect layers and a thick underlying silicon layer. Electrical isolation of the silicon fingers is realized with a slight silicon undercut etch, which disconnects sufficiently narrow pieces of silicon under the CMOS microstructures. The 1 mm by 1 mm micromirror is made of an approximately 40 μm-thick single-crystal silicon plate coated with aluminum from the CMOS interconnect stack. The mirror has a peak-to-peak curling of 0.5 μm. Fabrication starts with a conventional CMOS process followed by dry-etch micromachining steps. There is no need for wafer bonding and accurate front-to-backside alignment. Such capability has potential applications in biomedical imaging, optical switches, optical scanners, interferometric systems, and vibratory gyroscopes.