Development of SiC-based Gas Sensors for Aerospace Applications
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Development of SiC-based Gas Sensors for Aerospace Applications G. W. Hunter, P. G. Neudeck, J. Xu, D. Lukco1, A. Trunek2, M. Artale3, P. Lampard3, D. Androjna3, D. Makel4, B. Ward4, and C. C. Liu5 NASA Glenn Research Center, Instrumentation and Controls Division 21000 Brookpark Road, M/S 77-1, Cleveland OH 44135 1 QSS Group, Inc., Cleveland, OH 44135 2 OAI, Cleveland, OH 44135 3 Akima Corporation, Fairview Park, OH 44126 4 Makel Engineering, Chico, CA 95973 5 Case Western Reserve University, Cleveland, OH 44106 ABSTRACT Silicon carbide (SiC) based gas sensors have the ability to meet the needs of a range of aerospace applications including leak detection, environmental control, emission monitoring, and fire detection. While each of these applications require that the sensor and associated packaging be tailored for that individual application, they all require sensitive detection. The sensing approach taken to meet these needs is the use of SiC as a semiconductor in a Schottky diode configuration due to the demonstrated high sensitivity of Schottky diode-based sensors. However, Schottky diode structures require good control of the interface between the gas sensitive metal and SiC in order to meet required levels of sensitivity and stability. Two examples of effort to better control the SiC gas sensitive Schottky diode interface will be discussed. First, the use of chrome carbide as a barrier layer between the metal and SiC is discussed. Second, we report the first use of atomically flat SiC to provide an improved SiC semiconductor surface for gas sensor deposition. An example of the demonstration of a SiC gas sensor in an aerospace applications is given. It is concluded that, while significant progress has been made, the development of SiC gas sensor systems is still at a relatively early level of maturity for a number of applications. INTRODUCTION Silicon carbide (SiC) has high potential as the electronic semiconductor material for a new family of high temperature sensors and electronics. Silicon carbide can operate as a semiconductor in conditions under which silicon cannot adequately perform, such as at temperatures above 400°C or in corrosive environments. [1]. One area where SiC semiconductor technology can be applied is in chemical sensing. Silicon carbide gas sensors have been in development for a number of years using a range of designs including capacitors [2], transistors [3], and Schottky diodes [4-7]. These sensors have been shown to be highly sensitive to several gases, including hydrogen and hydrocarbons, making them useful for a range of applications. A range of aerospace applications require chemical sensing technology [8]. One application area is the monitoring of fuel leaks in launch vehicles. Detection of low concentrations of hydrogen and hydrocarbon fuels is critical in avoiding explosive conditions that could harm personnel and damage the vehicle. Reliable vehicle operation also depends on the timely and
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accurate measurement of these leaks. Detection of low concentrations of f
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