MEMS Processing Investigation Of 4H-SiC Piezoresistive Pressure Transducer

Pressure monitoring during deep-well drilling, automobiles and jet engines requires pressure transducers that can operate reliably at temperatures between 200oC and 600oC. Conventional silicon(Si) piezoresistive pressure transducers increasingly suffer instability and failure as the operation is extended toward higher-temperature regimes. The high-temperature failures include high leakage current of pn junction, degradation of metal/semiconductor contacts and weakening of wire-bonds caused by temperature-driven intermetalic diffusion. Silicon carbide(SiC) is the preferred semiconductor for electronic devices that work in harsh environments due to its excellent semiconductor properties, such as wide band gap and high critical breakdown field strength. SiC also exhibits excellent thermal and mechanical properties at high temperature, together with its fairly large piezoresistive coefficients, which makes it well-suited for use in the fabrication of high temperature electromechanical transducers. Some efforts have been made to develop pressure transducers on SiC materials.The emphasis of this master thesis focuses on the key technology investigation of 4H-SiC chip of piezoresistive pressure transducer. The fabrication process is optimized and the processing parameters of each process, such as preparation of diaphragm and the sensitive resistance, contact window, ohmic contact and wiring bond layer, are established after extensively comparative investigations. Through the process integration and mask plating design, the process flow is determined, and the 4H-SiC pressure transducer chip is fabricated.The glass ring for chip packaging is designed. The 4H-SiC transducer is gauge pressure type. The sensitivity is 2 μV/V/kPa, 2.5 μV/V/kPa and 4.7 μV/V/kPa when the full scale output(FSO) is 1 MPa, 2 MPa and 3 MPa, respectively, at room temperature.