Characterization of Electrostatic Micromembrane Actuator Performance Using a Mass Probing Method

Abstract

ABSTRACTWe describe a mass probing technique for characterizing the electro-mechanical behavior of micromembrane array actuators under electrostatic loads. The technique utilizes one or more arrays of center-positioned posts as a joint-link between an array of micro membrane actuators and a top movable rigid mass plate to generate 1D motion of the top mass owing to motion transfer from the deformed membranes. The micromembrane actuator arrays are fabricated using a stacked architecture similar to MUMPs in which the poly-Si structure material is replaced by metal-over-polymer composite, and final release is accomplished by a dry etch of a-Si sacrificial material. The mass probing technique is implemented by hybrid integrating a thick (100∼650-μm), heavy, and rigid mass plate (with a polished surface as a reflective mirror) onto the membrane array in which individual membrane actuators have a center interface post to act as mechanical linkage. A preliminary test of a 40-um pitch membrane array shows a 1st natural frequency of 2.1MHz of the membrane actuator. This was scaled down to ∼50KHz by a 2.7mmx2.7mm 200-μm thick mass load weighting 3.3-mg. Ignoring the small membrane mass, the lumped spring stiffness is estimated to be ∼70-μN/μm per actuator (3248 40-μm actuators embedded beneath the probing mass). Thus, motion transfer principle from micro size actuators to macro size components was demonstrated.