Design optimization and implementation of a microgravity capacitive HARPSS accelerometer

This paper reports on the design optimization and implementation of a lateral capacitive accelerometer with high sensitivity and micro-g resolution, fabricated through the high-aspect ratio polysilicon and single-crystal silicon process on regular silicon wafers. A new implementation of vertical corrugation in silicon electrodes is developed to reduce the mechanical noise equivalent acceleration of the sensor. The predicted effect of corrugation on thermomechanical noise and also on static sensitivity is verified using ANSYS steady-state thermal simulation and FEMLAB linear stationary electrostatics analysis, respectively. The number of corrugated electrodes and the sense gap spacing is optimized to minimize the system (sensor + circuit) noise floor, while satisfying process and electronics limits. The open-loop differential sensitivity of a 60-μm-thick prototype accelerometer is measured to be 0.25 V/g equivalent to 4.5 pF/g over a 1-g range. The estimated total noise equivalent acceleration of the system (sensor + circuit) is 0.95 μg/√Hz in atmosphere.