Large Angle MEMS EO/IR Beamsteering

L. Starman, D. Torres, H. Hall and S. Dooley
U.S. Air Force Research Laboratory, Ohio, United States

Keywords: MEMS, beamsteering, COMSOL, imaging, electrothermal

This research effort is focused on the development of large angle, out-of-plane surface micromachined MEMS micromirror devices fabricated both in-house and in the MEMSCAP foundry, capable of tip/tilt and piston motion. The out-of-plane deflections are created using a series of stacked thin film materials i.e. SiO2, and aluminium, or SiN, polysilicon, and gold to create multilayer beam structures. The extrinsic residual stress resulting from the difference in coefficient of thermal expansion of these materials is the centerpiece to creating the required out of plain deflections. The beam actuators are arranged in the form of a pyramid to provide the required out-of-plane upward deflections of >400 μm to enable large angle beamsteering. Currently, the micromirrors undercarriage exhibit approximately ±18 deg mechanical beamsteering when a 30 mA bias is applied to a single actuator. Finite element modelling (COMSOL) was used to simulate the actuation structure to validate the fabrication processes and experimental results. The combination of our actuation system and the micromirror assembly comprise a single element in the development of high-deflection micromirror arrays exhibiting a fill factor greater than 90%. These high fill-factor MEMS micromirrors are envisioned as suitable for low power IRCM or UAV beamsteering applications.