Piezoresistive Position Sensing for the Detection of Hysteresis and Dielectric Charging in CMOS-MEMS Variable Capacitors

μA position sensing scheme for the detection of hysteresis and dielectric charging is presented. The sensing mechanism is based upon piezoresistance and is applied to an RF MEMS variable capacitor fabricated using a standard 0.35 μm CMOS process with MEMS postprocessing. The position sensor, based upon the piezoresistive property of the CMOS polysilicon layer, proves capable of detecting the effects of hysteresis and dielectric charging in the fabricated device. Potential applications of the sensing scheme include the mitigation of the effects of hysteresis and dielectric charging on MEMS variable capacitors through closed-loop control.