This is an excerpt from J. Wallace, M. Jackson, C. Rice and J. Bjelobrk, " Temperature Sensor Fabricated in Silicon Carbide," ECE 4522: Design II, Department of Electrical and Computer Engineering, Mississippi State University, May 2001:

For years, the push of technology has been to take existing products and make them smaller, lighter, more reliable, and more efficient. This push can be seen in the area of space travel, where system complexity far exceeds that of the common automobile or airplane. As detection can be can be closely related to problem prevention, NASA has expressed needs for new, innovative ways to detect temperature in the harsh space environment. Aircraft have used temperature sensors since the late 1930.s, but common temperature sensors will not stand up to the rigorous feat of space travel [1]. The most widely used semiconductor, silicon, has limited capabilities in the high temperature range [5]. This is where silicon carbide has emerged as the next semiconductor leader in demanding electronics applications where sensing of and operation in high temperatures is desired. It allows operation in extremely high temperatures, faster switching time, and lower resistance.

NASA currently has no available means to detect temperature, pressure, and vibration in harsh, high temperature environments using a single, small unit. In the interest of high temperature sensing, NASA has funded this project to help solve several problems involving high temperatures in the Space Shuttle program. Our project involves the design of the temperaturesensing portion of a single unit sensor, which will later be incorporated into a MEMS (Micro-Electro-Mechanical Systems) technology device. A wide bandgap, outstanding techniques properties, chemical inertness, and compatibility with silicon micromachining techniques make silicon carbide (SiC) the leading semiconductor material for MEMS in harsh environmental applications [10]. The material is superior to standard silicon, and offers new possibilities in sensing applications where such harsh environments exist. With its high temperature threshold, a silicon carbide sensing device will easily withstand the extreme conditions of rocket boosters, spacecraft reentry, as well as any other extremes that can be found in space [2].

The ability of the device to detect and withstand high temperatures is joined by many other factors. There is also a need for the sensor to offer a quick response time (a low temperature time constant) [7]. With equipment costs ranging in the millions, detecting problems in their early stages could mean the difference between a successful mission and a costly disaster. To aid in response time, a device manufactured in silicon carbide offers faster switching capability than that of silicon [3].

Self-heating is a problem with temperature sensors because self-heating must be compensated for in order to obtain accurate ambient measurements. The devices. total circuitry will contain active devices that raise the temperature above actual ambient [4]. The total increase above the ambient temperature may not increase greater than that of the tolerance of the device for correct operation to occur.

Silicon carbide sensors offer many advantages over present devices. Using the silicon carbide technology, we will fabricate a device that addresses problems such as those expressed by NASA. The device, having a high temperature range, quick response time, and small packaging will address NASA needs while adding efficiency to overall operation.