Investigation of strain gauges based on interdigitated Ba0.5Sr0.5TiO3 thin film capacitors

The demand for monitoring of strain is growing in high temperature and harsh environment systems. In this work, the thin film interdigitated capacitive strain gauges are fabricated using Ba0.5Sr0.5TiO3 (BST) as the dielectric and palladium-13 wt% chromium (PdCr) alloy as the electrodes, and the strain sensing characteristics of the thin film devices are investigated. It was found that the sensors showed low values of dissipation factor and stable capacitance over the frequency range from 15 kHz to 500 kHz at different temperatures. The temperature coefficient of capacitance (TCC) has been measured for temperature ranging from 25 °C to 480 °C so that the effect of temperature on the devices is known. At low temperature less than 150 °C the TCC is very small within 20 ppm/°C. With the temperature increasing, the TCC increased rapidly, and at 480 °C, the TCC was measured to be 3100 ppm/°C while is obviously less than that of typical thick film capacitors. The gauge factor (GF) of the interdigitated capacitive strain gauge at temperatures ranging from 25 °C to 400 °C to be about 3. The gauge also exhibits good linearity and sensitivity at applied large strains.