Micromachined Piezoresistive-Sensed Diaphragms for Infrasonic Monitoring

Micromachined, piezoresistive-sensed diaph- ragms are designed and fabricated specifically for infrasound sensing applications. Relatively large diaphragms, up to 6 mm \times6 mm, are fabricated to meet the high sensitivity requirements of infrasonic monitoring. A double-stack SOI wafer process is used, resulting in a streamlined two-mask process without the need for doping or ion-implantation. Pressure-sensitivities of diaphragms are studied using a custom static calibration set-up. The piezoresistance of longitudinal and transverse resistors are studied over a large pressure range of ±5,500 Pa so that the linear and nonlinear response regions of diaphragms are observed. Measurements are compared against a nonlinear finite element simulation-shown to accurately predict the sensor's behavior over a large response range.