Electromechanical Measurements and Modeling of a High-Performance Small-Area Ultra-Thin SOI MEMS Piezoresistive Pressure Sensor

A microelectromechanical system (MEMS) silicon-on-insulator (SOI) differential pressure sensor, integrating a Wheatstone full bridge with four thin monocrystalline Si mesa piezoresistors located at the edges of an ultrathin ( $2.5~\mu $ m) and miniaturized (0.18 mm2) Si3N4/SiO2 membrane, is thoroughly investigated by both electrical and mechanical measurements. A comprehensive model is proposed to analyze the physical phenomena and correlate the electrical and mechanical properties. The pressure sensor demonstrates excellent electrical and mechanical performances under positive backside differential pressure, that is, for upward deflection, at supply voltages of 5 and 10 V. Under 10 V, the output voltage exhibits a linear increase from 0 to 100 kPa, achieving a high sensitivity and a mechanical figure of merit of $0.461~\mu $ V/V/Pa and 2.56 ppm/Pa/mm2, respectively, with a full-scale (FS) total nonlinearity error (NL) up to 0.78% FS. Analyzing the topographic measurements by deflection-pressure and stress-strain methods, Young’s modulus and residual stress are extracted to be ~116 GPa and 82 MPa, respectively. According to a comprehensive model, the optimal electrical performance of the pressure sensor is attributed to a high strain increase with pressure thanks to an ultrathin miniaturized membrane and piezoresistors closer to the membrane bottom surface. The relatively high total nonlinearity is caused by a dominant mechanical nonlinearity, which can be reduced in the future by improving the gauge positions and alignment.