Laterally actuated torsional micromirrors for large static deflection

We report on the implementation of laterally electrostatically actuated, torsionally suspended silicon-on-insulator (SOI) micromirrors with a static optical deflection angle of over 40/spl deg/ peak-to-peak. Decoupling the actuator and mirror design allows for large actuator arrays, allowing large dc deflection angle and high resonant frequency to coexist in the same device. The micromirror structures are fully monolithic, micromachined from the front side and back side of an SOI wafer-device layer. In-plane actuation is transformed into out-of-plane motion and rotation, enabling integration of a wide variety of SOI-MEMS sensors, actuators, and micromirrors. When operated in resonance at 1321 Hz, a typical device measured up to 92/spl deg/ peak-to-peak optical deflection at 127 Vdc with 15 Vac amplitude.

I. Introduction

THE RECENT focus of the MEMS world on optical applications of micromachined devices has pushed the field out of surface micromachining technology [1]–[3]. This is mainly due to the need for very flat mirrors and the desire for the large actuation forces available using high aspect-ratio micromachining. Fig. 1. Conversion of lateral actuation to rotation by applying actuation at points displaced from torsional suspensions' shear centers. Torsional suspensions are etched to Upper-beam level, and actuation arms are etched to Lower-beam level to apply push–pull force transferred from adjacent in-plane actuators (not shown in the figure). Fig. 2. Fabrication schematic for three-level beam structures. Four masks, two on front- and two on back-side are prepared first, followed by back- and front-side DRIE high aspect ratio silicon etches. By moving to silicon-on-insulator (SOI) technology, the flatness issue is mostly ameliorated [4]. The biggest remaining obstacle in SOI MEMS is the demonstration of out-of-plane motion.