A CMOS-MEMS Micromirror With Large Out-of-Plane Actuation

This paper reports a high-aspect-ratio, silicon-based vertical comb drive used to actuate a micromirror. The large displacement is achieved by the curled-up comb drives. This high-aspect-ratio vertical comb drive uses the vertical capacitance gradient of the sidewall capacitor existing between comb fingers. The electrical isolation is realized by using the undercut of the deep Si etch. The 1 mm by 1 mm micromirror is made of an approximately 40 μm-thick single-crystal silicon membrane with aluminum coated on the surface. The mirror has a peak-to-peak curling of 0.5 μm. The mechanical rotation angle of the mirror is ±5°. The fabrication process is compatible with standard CMOS processes, and there is no need for wafer bonding and accurate front-to-backside alignment. Such capability has potential applications in optical switches, optical scanners, interferometric systems, and vibratory gyroscopes.