A 350 C piezoresistive n-type 4H-SiC pressure sensor for hydraulic and pneumatic pressure tests

It has been a challenge to develop pressure sensors that can work in harsh environments. In this work, a piezoresistive n-type 4H-SiC pressure sensor is demonstrated, capable of working at 350 C under hydraulic and pneumatic pressure. The pressure measuring range of this sensor is 7 MPa and the chip dimension is 2.5 mm 2.5 mm 0.23 mm. A reliable Ti/TaSi₂/Pt metal ohmic contact is used in the sensor and experimental results show that the metal combination can withstand a wide temperature range of 30 C-350 C. In order to avoid thermal stress induced by the mismatch of thermal expansion coefficients of different packaging materials when increasing temperature, a double-layer bonding scheme of cement glue and epoxy is proposed. The inner layer of the chip and the kovar alloy base are directly bonded with the epoxy, while the outer layer is wrapped with the high-temperature cement glue. Experiments confirm that this method can achieve reliable packaging with temperatures up to 350 C for 5 h. Based on the above key technologies, the sensitivity of this sensor can reach 13.2 mV V^-1 kPa^-1 and the test data exhibit high linearity and repeatability. Static tests prove that the sensor has good media compatibility which can operate under a hydraulic pressure load at 220 C and a barometric pressure load under 350 C. The sensor in this work can provide a reference for pressure measurements at high temperature and in complex media environments.