Toward ultrasensitive MEMS electric field sensor based on bistable frequency domain width readout

A frequency difference readout approach based on the bistable frequency domain (BFD) width is proposed for high-sensitivity MEMS electric field sensing. The proposed method employs the frequency difference between the forward and backward jump points in the nonlinear amplitude frequency response as the sensing metric. A reduced-order nonlinear model is developed to describe the electric field dependent modulation of the BFD width. The sensor is fabricated using the SOIMUMPs process and experimentally characterized with a calibrated electric field generation setup. Experimental results show good linearity from 50 kV/m to 250 kV/m. As the AC drive voltage increases from 40 mV to 70 mV, the sensitivity increases from 0.215 Hz/(kV/m) to 0.913 Hz/(kV/m), indicating that the AC drive amplitude can serve as an effective tuning parameter for BFD width readout. Closed-loop frequency tracking further shows enhanced frequency stability in the nonlinear regime, with a normalized bias instability on the order of 10⁻⁹ and an estimated electric field resolution of 0.97 V/m at an AC drive voltage of 50 mV. These results demonstrate that BFD width readout provides a promising nonlinear sensing mechanism for high-sensitivity MEMS electric field sensing.