Sputter Deposition of Strain Gauges Using ITO/Ag

In many industrial applications strain gauges are commonly used for measurements of applied forces or the loading status of work pieces. While commercial strain gauges using polyimide foils can cause errors due to influence of humidity, directly applied thin film strain gauges avoid this problems. Besides the improvement of the signal due to avoiding glue and polymer substrate, that can creep and swell, also the gauge factor can be further improved by using new sensor materials. Indium tin oxide (ITO) is a very promising material especially for high temperature application. This paper presents investigations of Ag doped ITO films. The sheet resistance of the films increased first with increase in the silver content up to 20 at.-%. Further increase in silver led to a decrease in the sheet resistance reaching less than 10 D for more than 75 at.-% silver content of the resulting films. The gauge factor showed a maximum of 6.5 at 20 at.-% Ag content, while the temperature coefficient of resistance (TCR) showed zero crossing for approximately 40 at.-% Ag content.