High-temperature semiconductor transistor electronics capable of prolonged 500 °C operation would enable important advancements in the sensing and control of combustion in jet engines, making them cleaner, safer, and more fuel-efficient. In addition, such electronics are keys to the long-term operation of scientific probes on or near the scorching 460 °C surface of Venus. Although there have been reports of short-term (less than 10 hr) transistor operation at 500 °C or above, much longer operating times are needed for these and other beneficial high-temperature electronics applications. Toward this end, the NASA Glenn Research Center has been pioneering silicon carbide (SiC) semiconductor transistors and ceramic packaging technology targeted for greatly prolonged operational durability at 500 °C. These efforts previously demonstrated high-temperature chip- and board-level packages for prolonged 500 °C operation (refs. 1 and 2) and 2000 hr of 500 °C operation of an SiC metal-semiconductor field effect transistor (MESFET) (refs. 3 and 4) based on high-temperature ohmic contact technology (ref. 5).
Building on this foundation, civil servants and Ohio Aerospace Institute (OAI) researchers at Glenn designed, fabricated, and electrically operated continuously at 500 °C for more than 600 hr a high-temperature amplifier circuit based on an SiC MESFET, epilayer resistors, and a ceramic packaging system. This is the first semiconductor-based amplifier to demonstrate stable continuous electrical operation in such a harsh high-temperature oxidizing air environment with excellent stability over such an extended period of time.
Circuit diagram of a common-source amplifier circuit operated for more than 600 hr at 500 °C. The elements within the dotted box were operated in the 500 °C air-ambient oven; drain bias, VDD = 120 V; gate bias voltage, Vgate bias = -9 V; substrate bias voltage, Vsubstrate bias = -20 V; external coupling capacitor, Cext = 0.47 μF; gate resistance, RG = 150 kΩ; drain resistance, RD = 340 kΩ; drain current, ID.
Long description of figure 1.
The circuit schematic diagram shows the simple common-source amplifier circuit, which consists of an SiC MESFET, two SiC resistors, and a ceramic capacitor. The components inside the dotted lines of the diagram were packaged onto the ceramic high-temperature circuit board (see the following photograph), which was operated at 500 °C inside an oven. The circuit board with components was subjected to 656 hr of unbiased 500 °C heat soaking prior to initiation of the 500 °C continuous electrical operation. For this initial low-frequency demonstration, an external (room temperature) coupling capacitor was used to obtain sufficient coupling of the input signal because the 500 °C onboard capacitor was not designed to support circuit operation at frequencies as low as ~100 Hz.
Circuit-board assembly used for the long-duration 500 °C demonstration of the SiC transistor-based amplifier circuit.
Long description of figure 2.
The final figure shows the input (1-V peak-to-peak amplitude) and output (7-V peak-to-peak) sine voltage waveforms measured during the 430th hour of continuous electrical operation at 500 °C. Circuit power supply biases were not changed throughout the 500 °C electrical test duration. The amplifier gain remained stable (near 7) for over 600 hr of continuous 500 °C electrical operation (over 1300 hr of total soak time at 500 °C). After this time period, amplifier gain degradedsignificantly because of thermal annealing of the MESFET gate contact (ref. 4). Modifying the design of the SiC transistor (changing from a metal-semiconductor gate junction to a p-type/n-type semiconductor gate junction) should eliminate this gradual degradation mechanism. Nevertheless, this demonstration of 500 °C durability of a transistor-based amplifier circuit represents an important step toward significantly expanding the operational envelope of sensor signal-processing electronicsfor harsh environments such as the high-temperature regions of combustion engines and the surface of Venus.
Input (1-V peak-to-peak) and output (7-V peak-to-peak) sine waveforms recorded during the 430th hour of electrical operation of the amplifier stage at 500 °C.
Long description of figure 3.
Find out more about silicon carbide electronics research at Glenn: http://www.grc.nasa.gov/WWW/SiC/
Dr. Philip G. Neudeck, 216-433-8902, Philip.G.Neudeck@nasa.gov
Dr. Robert S. Okojie, 216-433-6522, Robert.S.Okojie@nasa.gov
Dr. Glenn M. Beheim, 216-433-3847, Glenn.M.Beheim@nasa.gov
Ohio Aerospace Institute (OAI)contacts: David J. Spry, 216-433-3361, David.J.Spry@nasa.gov
Dr. Liang-Yu Chen, 216-433-6458, Liangyu.Chenemail@example.com
Authors: Dr. Philip G. Neudeck and Dr. Liang-Yu Chen
Headquarters program office: Aeronautics Research Mission Directorate
Programs/projects: Glennan Microsystems Initiative, Propulsion 21, Ultra Efficient Engine Technology, NASA Electronic Parts and Packaging
Power and Electric Propulsion
Last updated: December 17, 2007
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