Capacitance response and strain sensing properties of barium titanate thin film*

Strain gauges are devices that convert mechanical stress into an electronic signal. In this research, barium titanate (BaTiO$_{3})$ films were deposited on flexible borosilicate glasses using a sol-gel method. Interdigitated electrodes were patterned on the films to fabricate a strain gauge. The strain gauge comprised of an array of individual coplanar capacitors on a 1.2x0.4 cm rectangular borosilicate glass of 0.16 mm thickness. A parallelogram clamp and a mechanically amplified piezoelectric actuator were used for supporting the device under test and for the application of the strain, respectively. Measurements of the strain were carried out on a cantilever beam by monitoring the changes in device capacitance and the frequency shift of an oscillator circuit. We obtained the frequency change per unit stress equal to 0.00163 MHz/MPa and the frequency change per unit strain equal to 1.038x10$^{-4}$ MHz/unit strain, respectively.