Fabrication of High Temperature Ceramic Pressure Sensor and Its Characteristics

This paper describes the fabrication process and characteristics of a micromachined ceramic pressure sensor based on tantalum nitride (Ta-N) thin film strain gauges that could be used in high temperature applications. The proposed micropressure sensor consisted of Ta-N thin film which was patterned in Wheatstone bridge configuration and sputter-deposited on thermally oxidized, micromachined Si diaphragms with a buried cavity for overpressure tolerance and an Al/Au interconnection layer. This device takes advantage of mechanical properties of single crystalline Si which was used as a diaphragm and made by Si-wafer direct bonding (SDB) and electrochemical etch-stop technology. Moreover, in order to extend range of operating temperatures, Ta-N thin film was used as a sensing element because, compared to other strain gauges, it has the relatively higher electrical resistivity, p = 768.93 muOmegaldrcm, higher stability and gauge factor, GF = 4.12. The fabricated pressure sensor had low temperature coefficient of resistance, TCR = -84 ppm/degC, high sensitivity, low nonlinearity and excellent temperature stability. Sensitivity and maximum nonlinearity in temperature range of 25degC to 200degC were 10.97 -12.1 muV/Vpsi and 0.43 %FS, respectively. These qualities suggest that Ta-N ceramic pressure sensor is very suitable for development of low cost and high temperature integrated pressure sensors.