Single-crystal silicon micromirror array with polysilicon flexures

High-density micromirror arrays (1296 mirrors) have been fabricated with a process that combines the benefits of both bulk and surface micromachining. Arrays fabricated with this technique are characterized by optically flat mirrors characterized by radius of curvature (ROC) ∼1 m, spring constant uniformity (∼6%) across the array, and yields greater than 90%. Each array element consists of a mirror-in-gimbal structure that allows the mirror to rotate about two orthogonal axes when voltage is applied to electrodes beneath the mirror. A dry release process combined with through wafer etching and spin-cast polyimide is introduced as a simple, effective alternative to critical point drying for releasing the structures. Tilt angle measurements for these devices show stable angular range of ±5° (mechanical) at 160-170 V.