Investigation of robustness of a SiC MOMS pressure sensor in high pressure/temperature operation conditions

Abstract: Rigorous environmental policies and the need for higher fuel economy continuously demand new innovations in the combustion process of automotive engines. Consequently, there is an increasing necessity for active monitoring of the combustion event, and therefore, microsystems have started coming into play. This master thesis presents a prototype of a SiC (silicon carbide) MOMS (micro-opto-mechanical system) pressure sensor, developed by RISE (Research Institutes of Sweden AB), suitable for harsh environment, such as the combustion chamber of an automobile, which could allow a real-time monitoring of the combustion process and hence its active optimasation. SiC used in the sensor is known for its unique properties – it is almost as hard as diamond, has a high melting point, and is chemically inert, making it highly suitable for the combustion chamber environment, where high pressure, high temperature, and aggressive mixtures are an ordinary. The sensor operates as a Fabry-Perot interferometer, hence uses an opto-mechanical method of sensing of pressure; by involvement of fibres, it allows for keeping the elements of the setup for analysing of light signal away from harshness, while introducing relatively small losses. Other advantages of the device are its small size and large measuring range. The SiC MOMS pressure sensor, in its normal operation, is intended to sense high pressures at high temperatures. This master thesis explains its operating principle and validates its robustness to these harsh conditions. The results of a COMSOL simulation of membrane deflection under pressures from 0 to 160 bar, and of an experiment, so-called pressure response test, performed at a similar range of pressures on several specimens, are discussed. The impact of an annealing test, conducted on the sensor at ~1000 °C for 10 h, is presented. The vast majority of the specimens showed sensing capabilities after they had been exposed to these harsh conditions, which indicates the great potential of the sensor for working in a combustion chamber.