1993-04-01

Silicon Microsensors for Aerospace Condition Monitoring 931359

This paper provides several examples of silicon “micromachined” semiconductor sensors with which the authors are involved for aerospace condition monitoring. This and related work in MEMS (Micro Electro Mechanical Systems) has the potential to revolutionize condition monitoring in aerospace condition and “health monitoring” by (1) moving “smart” electronics out to the sensor chip itself and (2) combining a vast quantity and types of, not only electronic, but micromechanical sensing schemes into the silicon chip . Precisely formed cantilevers, gears, valves, microplumbing and even micro motors of the cross-section of a human hair can be fabricated on a single silicon microchip.Silicon is an excellent mechanical material with a yield strength several times that of stainless steel. Also silicon has excellent thermal properties , whereas compatible silicon dioxide (which we typically use in connection with silicon microelectronics patterning) is virtually a thermal insulator. Other compatible thin films such as silicon nitride or even diamond (which we can now grow) provide an increased variety of microelectromechanical tools which can be formed to specifications of submicron dimension (a human hair is about 100 microns in diameter).Silicon has not been thought of as a high temperature material because conventional microelectronics is limited pretty much to the military range because of leakage in p-n junctions. This has limited silicon electronic applications in some of the more harsh aerospace applications, however silicon as a material will function well above 1000C for many mechanical applications in hot aerospace arenas. At cryogenic temperatures (except for the liquid hydrogen to liquid helium range) many silicon microelectronic circuits can be made to function even better than at room temperatures.In this paper, we survey several micromachined sensors which we have under development for aerospace applications, such as a micro flowsensor for gases and liquids, a fatigue and crack detection and imaging microchip, a hydrogen and gas leak detection microsensor as an inverse microspectrometer, a “smart” vibration microsensor, silicon microactuators, and silicon micromachined pressure sensors for harsh environments.

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