Design and Fabrication of a Long-Arm Comb-Drive Rotary Actuator With Externally Mounted Mirror for Optical Applications

In this paper, we present the design, fabrication, and characterization of a long-arm comb-drive actuator with an externally mounted large mirror for optical applications. The provision for an externally mounted mirror can be useful for many optical applications, which require large and high-quality reflecting surfaces. The angular stretch of the comb fingers at the far end is kept smaller than those near the anchor point. This structural feature allows the design of actuator arm lengths of over 5 mm. The truss of the actuator is designed carefully to support the large movable arm. An analytical model for the electrostatic forces in the actuator was developed, and detailed analyses for side instability and resonance frequency were performed. The complete fabrication process involving bulk micromachining of silicon-on-insulator (SOI) wafer using a two-mask process is described. A procedure for efficient mounting of the mirror utilizing die bonder, vacuum tip, and silver epoxy is demonstrated. Static characterization measurements show that the actuator can achieve a rotational angle of 3° with an applied voltage of 130 V. A resonance frequency of ~246 Hz for a mirror size of 2 mm × 100 μm × 1 mm was determined by optical characterization; this closely matches with the simulation results and the analytical model.