TPMS (tire-pressure monitoring system) sensors: Monolithic integration of surface-micromachined piezoresistive pressure sensor and self-testable accelerometer

Abstract

A novel surface-micromachining technology is developed to monolithically integrate piezoresistive pressure sensor and accelerometer for tire-pressure monitor system (TPMS) applications. A narrow rectangular diaphragm piezoresistive pressure sensor and a clamped beam-mass piezoresistive accelerometer compose the monolithic composite sensor that are on-chip integrated in a 1.6 mm × 1.6 mm single chip for low-cost production. With an electroplated Cu seismic-mass, the sensitivity of the accelerometer is much improved so that it can be compatibly fabricated with the pressure sensor by using surface-micromachining processes. For facilitating on-chip known-good-die and reliable TPMS application, the electroplated metal mass is used as a versatile structure to realize electrostatic self-testing function for the accelerometer. The fabricated TPMS sensors are characterized, resulting in 83.6 mV/MPa/3 V sensitivity and 0.34% FSO linearity for the 450 kPa-ranged pressure sensor, as well as, 15.6 μV/g/3 V sensitivity for the 125 g-ranged accelerometer. In addition, the on-chip electrostatic self-testing function is experimentally validated for the accelerometer.