A High Speed Electrostatically Actuated Al-MEMS Micromirror Array

The design of an electrostatically-actuated, aluminum, torsional micromirror, on the order of 20x20 microns, is presented. The design is repeated in 25x25 arrays for high-speed deflection of incident light as an optical shutter. Future designs would include individually addressable micromirror elements. Parameterization of geometries is described and the resulting optimized micromirror design is detailed. The COMSOL Multiphysics finite element analysis environment is utilized to study the optimized design. Within the finite element analysis software, a 132 V electric potential is applied to an underlying electrode in order to produce a minimum of 5° tilt which yields a downward mirror-edge displacement of 1.39 μm into a 4 μm gap between the electrode and the bottom of the micromirror. When the electric potential is removed, it is shown that the micro-mirror has a settle time ~10 μs. The prototypical micromirror arrays are fabricated using an Al-MEMS fabrication process. The developed fabrication process uses a 4 micron sacrificial photo-definable polymer and a submicron thick aluminum layer suspended over patterned gold electrodes. The sacrificial polymer was plasma-ashed to release the deformable aluminum structures.