Study of electrostatic actuated MEMS biaxial scanning micro-mirror with comb structure

Abstract

MEMS based actuator and scanning mirrors are device that steers and reflects incident light by angular rotation of the mirror itself. For single axis scanning, the mirror itself provides the required angular rotation, while most of the biaxial scanning micro mirrors have a gimbal configuration. Electrostatic actuation is commonly being used because of ease of fabrication and work on the principle of electrostatic forces between pairs of movable and fixed electrodes. Parallel plate type tip-tilt/scanning mirror is commonly being used for smaller mirror dimensions (up to 2mm). For larger mirror diameter (>2mm), the desired scan angle leads to large gap between the electrodes, which increases the driving voltage drastically and leads to bulky driver controller. Alignment between fingers is essential to avoid lateral instability causing an in-plane rotational pull-in during an actuation. To reduce the driving voltage, the straight torsion springs which connect the mirror to the gimbal are replaced by comb structures. It finds applications in optical MEMS (OMEMS) [1, 2], digital light projector, optical switch, adaptive optics, communications, signal sensing, and confocal microscopes. In this paper, design, simulation of electrostatic actuation based parallel plate comb type two axis tilt scanning micro mirror is described. The effect of comb structure on pull-down voltage and resonant frequency is studied.