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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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    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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  • 4
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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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  • 5
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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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  • 6
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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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  • 7
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    Surface and Interface Properties of PdCr/SiC Schottky Diode Gas Sensor Annealed at 425 C (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    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(x)Si only in a very narrow interfacial region. After annealing for 250 hours at 425 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. 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
    Format: application/pdf
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  • 8
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    Electronic and Interfacial Properties of PD/6H-SiC Schottky Diode Gas Sensors (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Pd/SiC Schottky diodes detect hydrogen and hydrocarbons with high sensitivity. Variation of the diode temperature from 100 C to 200 C shows that the diode sensitivity to propylene is temperature dependent. Long-term heat treating at 425 C up to 140 hours is carried out to determine the effect of extended heat treating on the diode properties and gas sensitivity. The heat treating significantly affects the diode's capacitive characteristics, but the diode's current carrying characteristics are much more stable with a large response to hydrogen. Scanning Electron Microscopy and X-ray Spectrometry studies of the Pd surface after the heating show cluster formation and background regions with grain structure observed in both regions. The Pd and Si concentrations vary between grains. Auger Electron Spectroscopy depth profiles revealed that the heat treating promoted interdiffusion and reaction between the Pd and SiC dw broadened the interface region. This work shows that Pd/SiC Schottky diodes have significant potential as high temperature gas sensors, but stabilization of the structure is necessary to insure their repeatability in long-term, high temperature applications.
    Keywords: Instrumentation and Photography
    Type: NASA-TM-107255 , E-10316 , NAS 1.15:107255 , International High Temperature Electronics Conference; Jun 09, 1996 - Jun 14, 1996; Alburquerque, NM; United States
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