Survivability of a silicon-based microelectronic gas-detector structure for high-temperature flow applications

This investigation addresses the important question of whether or not silicon-based micromachined chemical sensors are a viable option for gas sensing in harsh, high-temperature flow applications such as automotive exhaust. Data are presented on the thermal and mechanical stability and long-term functionality of micromachined silicon devices containing ultra-thin Pt/TiOx films supported on a heated multilayer silicon oxide/silicon nitride membrane. These gas detectors were originally designed for use in vacuum applications such as reactive ion etching systems. Significant modifications in device structure and materials are required to adapt these sensors for use in harsh thermal and chemical environments at elevated pressures. To test the long-term. structural integrity of the sensors, they are subjected to a test protocol including pressure fluctuations, thermal shock, and mechanical vibrations. For characterization purposes, electrical resistance measurements, optical microscopy, atomic force microscopy (AFM), and Auger spectroscopy have been used. Our results indicate that properly designed micromachined silicon structures can survive long-term operation at high temperatures in ambient air, and can withstand rapid fluctuations of temperature, pressure, and flow rate.