Monolithic pressure+acceleration sensor with self-test function for reliable & low-cost tire-pressure-monitoring-system (TPMS) applications

Reported is a surface-micromachined piezoresistive composite sensor, with both pressure sensor and accelerometer integrated in a 1.6mm×1.6mm chip for low-cost automobile tire-pressure monitor system (TPMS) application [1]. The two sensors are fabricated with compatible surface-micromachining process. Using a LIGA like process, a Cu thick-layer is electroplated and patterned on the accelerometer mass region to improve sensitivity. A self-test function is designed for the accelerometer to monitor the mechanically fragile sensor for reliable application. By detecting the wheel-rotation induced centrifugal acceleration, a -25g~+125g accelerometer is used to wake-up a 550kPa-ranged pressure sensor in a power-saving mode. The fabricated pressure sensor has a sensitivity of 0.08mV/KPa under 3V power supply and the linearity is about 0.3%FS. The sensitivity of the acceleration sensor is tested as 30μV/g.