Torsion-mirror actuators with compound electrostatic driving structures

A novel kind of torsion-mirror actuator with compound electrostatic driving structures is reported. The actuators are fabricated in SOI wafers through a newly developed set of surface-and-bulk-mixed-silicon-micromachining processes. the advanced compound driving structures are made up of plate-electrode coupled drives and vertical comb drives. Measurements and analyses indicate that the compound driving structures are able to decrease by about 34% the yielding voltages for actuating the mirrors to achieve 90° rotation. The micro-mirrors of the actuators can cyclically vibrate a few 10⁶ times, at least, between 0° and 90°, and the shortest actuating time they can reach is estimated to be less than 2.5 ms. In regard to the actuators, a theoretical model of the intrinsic frequency of the tilting vibration of their movable structures is obtained. According to the model, the frequency is a nonlinear function of the rotation angle of the mirrors.