Stretched-film micromirrors for improved optical flatness

We have developed a new tensile optical-surface (TOS) process to produce optically flat micromirrors capable of scanning at high frequencies. A polysilicon membrane is stretched across a stiff, single-crystal silicon-rib structure. This structure increases the stiffness of the mirror without significantly increasing its mass. The low mass makes possible high operating frequencies without deformation that could significantly compromise the optical performance of the mirror. Electrostatic comb drives, made of thick single-crystal silicon, provide large forces that enable mirror operation at tens of kHz.