Dynamic deformation of stretched membrane in drum-type micromirror

Realizing an optically flat surface during high-speed scanning is a crucial factor for the micromirror with large mirror plate. This paper presents the dynamic deformation analysis of stretched polycrystalline (poly-) Si membrane of flat and lightweight drum-type micromirror. The drum-type micromirror is realized using a tense poly-Si membrane across a rigid crystalline (c-) Si ring. The total peak-to-valley surface deformation realized in the designed micromirror is about 50 nm and observed on the connecting part between the c-Si ring and the poly-Si membrane. The stress concentration in this connecting part is investigated using the amount of surface distortion. The amount of the dynamic deformation in the poly-Si membrane is less than 40 nm. This satisfies the optical flatness compared to the wavelength of blue light.