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Characteristics of a Reactively Sputtered Indium Tin Oxide Thin Film Strain Gage for Use at Elevated Temperatures

  • Otto J. Gregory (a1), Stephen E. Dyer (a1), Paul S. Amons (a1) and Arnout Bruins SLOT (a1)

Abstract

Strain sensors based on thin films of indium tin oxide (ITO) have been developed for a variety of applications, where the measurement of both static and dynamic strain are required at elevated temperatures. ITO thin films were prepared by rf reactive sputtering in Ar:02 mixtures from high density, electrically conductive targets having a nominal composition of 90% In203 and 10% Sn02. The resulting ITO films exhibited room temperature resistivities between 2x10−2 and 2x102 ω cm, an optical bandgap of 3.5 ev and tested “n” type by hot probe. These same films exhibited large negative gage factors (G=δρ/ ρδε) when tested at room temperature and a relatively low temperature coefficient of resistance when tested at elevated temperature in air. Specifically, gage factors approaching -100 with little hysteresis were observed for strains up to 700 μin/in and TCR's as low as 195 ppm/°C have been measured for the sputtered ITO films. In addition, these films were electrically stable and readily formed ohmic contacts with platinum at temperatures up to 1180°C. In this paper, we report on the electrical properties and piezoresistive properties of ITO based strain gages at temperatures up to 1180°C. Prospects of using ITO thin films as the active strain elements in high temperature strain gages and the characteristics of strain sensors based on ITO are discussed.

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Characteristics of a Reactively Sputtered Indium Tin Oxide Thin Film Strain Gage for Use at Elevated Temperatures

  • Otto J. Gregory (a1), Stephen E. Dyer (a1), Paul S. Amons (a1) and Arnout Bruins SLOT (a1)

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