Gravity and Film Stress Analysis for Mems Deformable Mirror with Electrostatic Piston Array

This paper reports gravity and film stress effects on the up and down motion of a MEMS deformable mirror, actuated electrostatically by an array of pistons. To keep the inter-electrode gap small for efficient electrostatic force actuation, the pistons are located close to the underside of the mirror and move independently as the mirror deforms. The mirror membrane is 8 mm in diameter, 2µm thick and made of single crystal silicon. With a horizontal orientation the relatively large weight of the pistons, fabricated into thick silicon substrate, deform the mirror. However, by placing the device vertically, a bidirectional motion and upward displacement of 0.2 µm with 30 V actuation was confirmed. The cause of unexpected small, localized downward displacement, was also investigated via finite element analysis.