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  • 1
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    Surface and Interface Properties of PdCr/SiC Schottky Diode Gas Sensor Annealed at 425 C (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: The surface and interface properties of Pd(0.9,)Cr(0.1)/SiC Schottky diode gas sensors both before and after annealing are investigated using Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). At room temperature the alloy reacted with SiC and formed Pd,Si only in a very narrow interfacial region. After annealing for 250 h ,It 425 C, the surface of the Schottky contact area his much less silicon and carbon contamination than that found on the surface of an annealed Pd/SiC structure. Palladium silicides (Pd(x)Si) formed at a broadened interface after annealing, but a significant layer of alloy film is still free of silicon and carbon. The chromium concentration with respect to palladium is quite uniform down to the deep interface region. A stable catalytic surface and a clean layer of Pd(0.9)Cr(0.1) film are likely responsible for significantly improved device sensitivity.
    Keywords: Instrumentation and Photography
    Type: Solid-State Electronics (ISSN 0038-1101); Volume 42; No. 12; 2209-2214
    Format: text
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  • 2
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    SiC-Based Schottky Diode Gas Sensors (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-27
    Description: Silicon carbide based Schottky diode gas sensors are being developed for high temperature applications such as emission measurements. Two different types of gas sensitive diodes will be discussed in this paper. By varying the structure of the diode, one can affect the diode stability as well as the diode sensitivity to various gases. It is concluded that the ability of SiC to operate as a high temperature semiconductor significantly enhances the versatility of the Schottky diode gas sensing structure and will potentially allow the fabrication of a SiC-based gas sensor arrays for versatile high temperature gas sensing applications.
    Keywords: Instrumentation and Photography
    Type: NASA-TM-113159 , NAS 1.15:113159 , E-10910
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  • 3
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    Processing and Prolonged 500 C Testing of 4H-SiC JFET Integrated Circuits with Two Levels of Metal Interconnect (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Complex integrated circuit (IC) chips rely on more than one level of interconnect metallization for routing of electrical power and signals. This work reports the processing and testing of 4H-SiC junction field effect transistor (JFET) prototype ICs with two levels of metal interconnect capable of prolonged operation at 500 C. Packaged functional circuits including 3-and 11-stage ring oscillators, a 4-bit digital to analog converter, and a 4-bit address decoder and random access memory cell have been demonstrated at 500 C. A 3-stage oscillator functioned for over 3000 hours at 500 C in air ambient.
    Keywords: Solid-State Physics; Electronics and Electrical Engineering
    Type: GRC-E-DAA-TN27164 , International Conference on Silicon Carbide and Related Materials (ICSCRM 2015); Oct 04, 2015 - Oct 09, 2015; Sicily; Italy
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  • 4
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    SiC-Based Gas Sensors (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Electronic grade Silicon Carbide (SiC) is a ceramic material which can operate as a semiconductor at temperatures above 600 C. Recently, SiC semiconductors have been used in Schottky diode gas sensor structures. These sensors have been shown to be functional at temperatures significantly above the normal operating range of Si-based devices. SiC sensor operation at these higher temperatures allows detection of gases such as hydrocarbons which are not detectable at lower temperatures. This paper discusses the development of SiC-based Schottky diode gas sensors for the detection of hydrogen, hydrocarbons, and nitrogen oxides (NO(x)). Sensor designs for these applications are discussed. High sensitivity is observed for the hydrogen and hydrocarbon sensors using Pd on SiC Schottky diodes while the NO(x) sensors are still under development. A prototype sensor package has been fabricated which allows high temperature operation in a room temperature ambient by minimizing heat loss to that ambient. It is concluded that SiC-based gas sensors have considerable potential in a variety of gas sensing applications.
    Keywords: Instrumentation and Photography
    Type: NASA-TM-113125 , NAS 1.15:113125 , E-10891 , Oct 06, 1996 - Oct 11, 1996; San Antonio, TX; United States
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  • 5
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    Chemical Gas Sensors for Aeronautic and Space Applications (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Aeronautic and space applications require the development of chemical sensors with capabilities beyond those of commercially available sensors. Two areas of particular interest are safety monitoring and emission monitoring. In safety monitoring, detection of low concentrations of hydrogen at potentially low temperatures is important while for emission monitoring the detection of nitrogen oxides, hydrogen, hydrocarbons and oxygen is of interest. This paper discusses the needs of aeronautic and space applications and the point-contact sensor technology being developed to address these needs. The development of these sensors is based on progress in two types of technology: (1) Micromachining and microfabrication technology to fabricate miniaturized sensors. (2) The development of high temperature semiconductors, especially silicon carbide. The detection of each type of gas involves its own challenges in the fields of materials science and fabrication technology. The number of dual-use commercial applications of this microfabricated gas sensor technology make this general area of sensor development a field of significant interest.
    Keywords: Instrumentation and Photography
    Type: NASA-TM-107444 , NAS 1.15:107444 , E-10714 , Sensors Expo 1997; May 12, 1997 - May 15, 1997; Boston, MA; United States
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  • 6
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    Development of High Temperature Gas Sensor Technology (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The measurement of engine emissions is important for their monitoring and control. However, the ability to measure these emissions in-situ is limited. We are developing a family of high temperature gas sensors which are intended to operate in harsh environments such as those in an engine. The development of these sensors is based on progress in two types of technology: (1) The development of SiC-based semiconductor technology; and (2) Improvements in micromachining and microfabrication technology. These technologies are being used to develop point-contact sensors to measure gases which are important in emission control especially hydrogen, hydrocarbons, nitrogen oxides, and oxygen. The purpose of this paper is to discuss the development of this point-contact sensor technology. The detection of each type of gas involves its own challenges in the fields of materials science and fabrication technology. Of particular importance is sensor sensitivity, selectivity, and stability in long-term, high temperature operation. An overview is presented of each sensor type with an evaluation of its stage of development. It is concluded that this technology has significant potential for use in engine applications but further development is necessary.
    Keywords: Instrumentation and Photography
    Type: NASA-TM-107442 , NAS 1.15:107442 , E-10710 , Turbo-Expo 1997; Jun 02, 1997 - Jun 05, 1997; Orlando, FL; United States
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  • 7
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    Surface and Interface Study of PdCr/SiC Schottky Diode Gas Sensor Annealed at 425 C (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The surface and interface properties of Pd(sub 0.9)Cr(sub 0.1/SiC Schottky diode gas sensor both before and after annealing are investigated using Auger Electron Spectroscopy (AES), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS). At room temperature the alloy reacted with SiC and formed Pd(sub x)Si only in a very narrow interfacial region. After annealing for 250 hours at 425 deg. C, the surface of the Schottky contact area has much less silicon and carbon contamination than that found on the surface of an annealed Pd/SiC structure. Pd(sub x)Si formed at a broadened interface after annealing, but a significant layer of alloy film is still free of silicon and carbon. The chromium concentration with respect to palladium is quite uniform down to the deep interface region. A stable catalytic surface and a clean layer of Pd(sub 0.9)Cr(sub 0.1) film are likely responsible for significantly improved device sensitivity.
    Keywords: Instrumentation and Photography
    Type: NASA/TM-1998-107429 , E-11155 , NAS 1.15:107429 , Dec 01, 1997 - Dec 05, 1997; Boston, MA; United States
    Format: application/pdf
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  • 8
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    6H-SiC Transistor Integrated Circuits Demonstrating Prolonged Operation at 500 C (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The NASA Glenn Research Center is developing very high temperature semiconductor integrated circuits (ICs) for use in the hot sections of aircraft engines and for Venus exploration where ambient temperatures are well above the approximately 300 degrees Centigrade effective limit of silicon-on-insulator IC technology. In order for beneficial technology insertion to occur, such transistor ICs must be capable of prolonged operation in such harsh environments. This paper reports on the fabrication and long-term 500 degrees Centigrade operation of 6H-SiC integrated circuits based on epitaxial 6H-SiC junction field effect transistors (JFETs). Simple analog amplifier and digital logic gate ICs have now demonstrated thousands of hours of continuous 500 degrees Centigrade operation in oxidizing air atmosphere with minimal changes in relevant electrical parameters. Electrical characterization and modeling of transistors and circuits at temperatures from 24 degrees Centigrade to 500 degrees Centigrade is also described. Desired analog and digital IC functionality spanning this temperature range was demonstrated without changing the input signals or power supply voltages.
    Keywords: Solid-State Physics; Electronics and Electrical Engineering
    Type: GRC-WO-667828 , International Conference on High Temperature Electronics (HiTEC 2008); May 13, 2008 - May 15, 2008; Albuquerque, NM; United States
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  • 9
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    Confinement of Screw Dislocations to Predetermined Lateral Positions in (0001) 4H-SiC Epilayers Using Homoepitaxial Web Growth (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper reports initial demonstration of a cantilevered homoepitaxial growth process that places screw dislocations at predetermined lateral positions in on-axis 4H-SiC mesa epilayers. Thin cantilevers were grown extending toward the interior of hollow pre-growth mesa shapes etched into an on-axis 4H-SiC wafer, eventually completely coalescing to form roofed cavities. Each completely coalesced cavity exhibited either: 1) a screw dislocation growth spiral located exactly where final cantilever coalescence occurred, or 2) no growth spiral. The fact that growth spirals are not observed at any other position except the central coalescence point suggests that substrate screw dislocations, initially surrounded by the hollow portion of the pre-growth mesa shape, are relocated to the final coalescence point of the webbed epilayer roof. Molten potassium hydroxide etch studies revealed that properly grown webbed cantilevers exhibited no etch pits, confirming the superior crystal quality of the cantilevers.
    Keywords: Solid-State Physics; Electronics and Electrical Engineering
    Type: GRC-WO-667834 , 2002 Materials Research Society (MRS) Fall Meeting; Dec 02, 2002 - Dec 06, 2002; Boston, MA; United States|Materials Research Society Symposium Proceedings; o 742; K5.2.1-K5.2.6
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  • 10
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    Silicon Carbide Technology (2006)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Silicon carbide based semiconductor electronic devices and circuits are presently being developed for use in high-temperature, high-power, and high-radiation conditions under which conventional semiconductors cannot adequately perform. Silicon carbide's ability to function under such extreme conditions is expected to enable significant improvements to a far-ranging variety of applications and systems. These range from greatly improved high-voltage switching for energy savings in public electric power distribution and electric motor drives to more powerful microwave electronics for radar and communications to sensors and controls for cleaner-burning more fuel-efficient jet aircraft and automobile engines. In the particular area of power devices, theoretical appraisals have indicated that SiC power MOSFET's and diode rectifiers would operate over higher voltage and temperature ranges, have superior switching characteristics, and yet have die sizes nearly 20 times smaller than correspondingly rated silicon-based devices [8]. However, these tremendous theoretical advantages have yet to be widely realized in commercially available SiC devices, primarily owing to the fact that SiC's relatively immature crystal growth and device fabrication technologies are not yet sufficiently developed to the degree required for reliable incorporation into most electronic systems. This chapter briefly surveys the SiC semiconductor electronics technology. In particular, the differences (both good and bad) between SiC electronics technology and the well-known silicon VLSI technology are highlighted. Projected performance benefits of SiC electronics are highlighted for several large-scale applications. Key crystal growth and device-fabrication issues that presently limit the performance and capability of high-temperature and high-power SiC electronics are identified.
    Keywords: Solid-State Physics; Electronics and Electrical Engineering
    Type: GRC-WO-667841
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