Differential capacitive position sensor for planar MEMS structures with vertical motion

Ž . A capacitive sensor has been developed for measuring the vertical deflection of bridge-type micro-electromechanical MEMS silicon actuators. The sensor requires no electrodes above the actuator surface and does not require the actuator diaphragm to be used as a signal electrode. Sets of interdigitated electrodes, one for ac signal injection and the other for signal sensing, are placed beneath the actuator membrane. As the actuator deflects, the capacitance between the interdigitated finger electrodes is altered, leading 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, thereby providing a measure of actuator displacement in the direction perpendicular to the silicon substrate. Signal voltages on the order of 10 mV per 1 mm of deflection are observed for deflections in the 1-mm range. q 2000 Elsevier Science S.A. All rights reserved.