New SiC Pressure-Sensor-Technologies for Harsh Environments

Abstract:
A new technology for low cost MEMS-pressure sensors based on silicon carbide (SiC) for harsh environment applications has been developed. The main MEMS pressure transduction principles, piezoresistive and capacitive, are not well suited for harsh environments especially when high temperatures are present. Conventional silicon piezoresistors suffer from current leakage at temperatures above ~150deg C. SOI based piezoresistive sensors are limited to ~450deg C because of plastic deformation of the silicon membrane beyond this temperature. Silicon carbide as advanced MEMS material allows piezoresistive pressure measurement at much higher temperatures, however the gauge factor is drastically lower than for silicon and shows a temperature dependence. Capacitive methods on the other hand are highly susceptible to parasitic capacitances, and the signal processing needs to be close to the sensor element which is impractical due to the high temperature environment. This paper shows the technolgies for an absolute pressure sensor with membrane microcontact capable of operation in harsh environments with corrosive media and temperatures up to 900deg C.