Development of the invar36 thin film strain gauge sensor for strain measurement

This paper presents development of invar36 thin film strain gauges of various thicknesses ranging from 100 to 1400 Å for strain measurement. The strain gauges are deposited on microslides using the dc magnetron sputtering technique. Resistivity, temperature coefficient of resistance (TCR) and gauge factors of all gauges are measured and compared with each other. TCR is estimated by systematic annealing of gauges in vacuum and found as low as 190 ppm °C⁻¹. A four-point bending setup is designed and fabricated to measure the gauge factors of all gauges. The gauge factor of relatively thinner strain gauge is found as high as 4.5 and for strain gauges with thickness greater than 500 Å gauge factor is found less than 2.5. The variations of gauge resistance with applied strain are studied in terms of linearity, hysteresis and repeatability. The developed strain gauges are connected in a full-bridge configuration and the output response to the applied strain is studied at different excitation voltages. (paper)