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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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    Electrical Characterization of 4H-SiC JFET Wafer: DC Parameter Variations for Extreme Temperature IC Design (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This work reports DC electrical characterization of a 76 mm diameter 4H-SiC JFET test wafer fabricated as part of NASA's on-going efforts to realize medium-scale ICs with prolonged and stable circuit operation at temperatures as high as 500 degC. In particular, these measurements provide quantitative parameter ranges for use in JFET IC design and simulation. Larger than expected parameter variations were observed both as a function of position across the wafer as well as a function of ambient testing temperature from 23 degC to 500 degC.
    Keywords: Electronics and Electrical Engineering; Solid-State Physics
    Type: GRC-E-DAA-TN16537 , 2014 European Conference on Silicon Carbide and Related Materials; Sep 21, 2014 - Sep 25, 2014; Grenoble; France
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  • 4
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    SiC Technology (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Silicon carbide (SiC)-based semiconductor electronic devices and circuits are presently being developed for use in high-temperature, high-power, and/or 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 [1- 4] for energy savings in public electric power distribution and electric motor drives to more powerful microwave electronics for radar and communications [5-7] 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 realized in experimental SiC devices, primarily due 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 [9]. This chapter briefly surveys the SiC semiconductor electronics technology. In particular, the differences (both good and bad) between SiC electronics technology and 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/or high power SiC electronics are identified.
    Keywords: Electronics and Electrical Engineering; Solid-State Physics
    Type: GRC-WO-667840
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  • 5
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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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  • 6
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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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  • 7
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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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  • 8
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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
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  • 9
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    Evidence of Processing Non-Idealities in 4H-SiC Integrated Circuits Fabricated with Two Levels of Metal Interconnect (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The fabrication and prolonged 500 C electrical testing of 4H-SiC junction field effect transistor (JFET) integrated circuits (ICs) with two levels of metal interconnect is reported in another submission to this conference proceedings. While some circuits functioned more than 1000 hours at 500 C, the majority of packaged ICs from this wafer electrically failed after less than 200 hours of operation in the same test conditions. This work examines the root physical degradation and failure mechanisms believed responsible for observed large discrepancies in 500 C operating time. Evidence is presented for four distinct issues that significantly impacted 500 C IC operational yield and lifetime for this wafer.
    Keywords: Electronics and Electrical Engineering; Solid-State Physics
    Type: GRC-E-DAA-TN26974 , International Conference on Silicon Carbide and Related Materials; Oct 04, 2015 - Oct 09, 2015; Sicily; Italy
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  • 10
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    An overview of silicon carbide device technology (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Recent progress in the development of silicon carbide (SiC) as a semiconductor is briefly reviewed. This material shows great promise towards providing electronic devices that can operate under the high-temperature, high-radiation, and/or high-power conditions where current semiconductor technologies fail. High quality single crystal wafers have become available, and techniques for growing high quality epilayers have been refined to the point where experimental SiC devices and circuits can be developed. The prototype diodes and transistors that have been produced to date show encouraging characteristics, but by the same token they also exhibit some device-related problems that are not unlike those faced in the early days of silicon technology development. Although these problems will not prevent the implementation of some useful circuits, the performance and operating regime of SiC electronics will be limited until these device-related issues are solved.
    Keywords: SOLID-STATE PHYSICS
    Type: NASA-TM-105402 , E-6803 , NAS 1.15:105402 , Symposium on Space Nuclear Power Systems; Jan 12, 1992 - Jan 16, 1992; Albuquerque, NM; United States
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