Surface-Micromachined Silicon Carbide Pirani Gauges for Harsh Environments

Abstract

The application of pressure sensors in harsh environments is typically hindered by the stability of the material over long periods of time. This work focuses on the design and fabrication of surface micromachined Pirani gauges which are designed to be compatible with state-of-the-art Silicon Carbide CMOS technology. Such an integrated platform would boost harsh environment compatibility while reducing the required packaging complexity. An analytical model was derived describing the design variables of the Pirani gauges followed by Finite Element Analysis. The Pirani gauges were fabricated in a CMOS compatible cleanroom with a process employing only three masks, thus suitable for mass production. The SiC-based Pirani gauge is far more competitive than the traditional Si-based Pirani gauge in terms of endurance in high-temperature environments. From 25°C to 650°C, the gauge shows a reproducible response to pressure changes and has a maximum sensitivity of $17.63~\Omega $ /Pa at room temperature, and of $1.23~\Omega $ /Pa at 650°C. Additionally, some of the gauges were demonstrated to operate at temperatures up to 750°C.