Differential capacitive position sensor for planar MEMS structures with vertical motion

A capacitive sensor has been developed for measuring the vertical deflectio n of bridge-type micro-electromechanical (MEMS) silicon actuators. The sens or requires no electrodes above the actuator surface and does not require t he actuator diaphragm to be used as a signal electrode. Sets of interdigita ted electrodes, one for ac signal injection and the other for signal sensin g, are placed beneath the actuator membrane. As the actuator deflects, the capacitance between the interdigitated finger electrodes is altered, leadin g to a change in the time-varying charge induced on the sense fingers. This change in induced charge is monitored by a current-to-voltage converter, t hereby providing a measure of actuator displacement in the direction perpen dicular to the silicon substrate. Signal voltages on the order of 10 mV per 1 mu m of deflection are observed for deflections in the 1-mu m range. (C) 2000 Elsevier Science S.A. All rights reserved.