Optimization designed large-stroke MEMS micromirror for adaptive optics

A novel micromirror based on the PolyMUMPs process is designed and presented. The hexagonal micromirror with a diameter of 450 mu m consists of three supporting bilayer cantilevers and a mirror plate. The bilayer cantilevers, formed with a polysilicon layer and a gold layer, elevate the mirror plate according to residual stress-induced bending. Both analytical and finite element analysis (FEA) models are built to calculate the elevated height of the free end of the cantilever. The analytical solution is in accordance with the FEA simulation results, with longitudinal stresses applied only. Results of a three-dimensional (3D) simulation with two direction stresses applied also show the elevated height to be proportional to the width of the cantilever and the length of the gold layer. Due to the torque of the joint, the elevated heights of the two kinds of cantilevers assembled with the mirror plates are much smaller than those of the free end of the cantilevers. Both micromirrors with different cantilevers are fabricated. The elevated heights of the fabricated micromirrors are measured using Veeco optical profiler, which show good coincidence with simulation results.