A Two-Row Interdigitating-Finger Repulsive-Torque Electrostatic Actuator and Its Application to Micromirror Vector Display

This paper presents a novel two-row interdigitating-finger repulsive-torque electrostatic actuator and its application to the micromirror vector display. The actuator consists of upper and lower rotation units and an output beam. Each unit has one row of rotation fingers, i.e., the lower and upper rotation fingers, which interdigitate with each other. The lower and upper rotation fingers are subject to different electric potentials. Each rotation finger and its underneath aligned fixed finger are subject to the same electric potential. The actuator generates repulsive torques to rotate the lower and upper fingers out-of-plane with the maximum rotation not limited either by the gap between fingers and the substrate nor by the pull-in effect. The output beam is connected to the lower row of rotation fingers, and therefore, the actuator has the same rotation as the lower unit. The actuator requires only two thin films and is suitable for surface micromachining. The model is established to verify the actuator and calculate its performance. Prototypes are fabricated and tested. The experimental results show that the actuator achieved a mechanical rotation of 11.5° at the static driving voltage of 150 V and a resonant frequency of 380 Hz with a sinusoidal driving voltage varying from 20 to 70 V. This paper demonstrates the application of the actuator in micromirror vector display. Four actuators are connected to the peripheries of a micromirror plate and independently controlled to drive the mirror plate to achieve quasi-static 2-D rotation. A laser beam is reflected and steered by the mirror plate to any desired direction to realize vector display. The prototype of the vector display micromirror is fabricated and tested. A vector display module integrating the micromirror, a laser, and a concave lens is built. Based on this module, an automotive head-up display system is developed, which is able to display the navigation map, speed, turning sign, and vehicle location on a translucent screen.