Simultaneous high-frequency measurement of direct and inverse transverse piezoelectric coefficients of thin films using longitudinal vibration

A setup and approach for simultaneous measurement of the inverse and direct transverse piezoelectric coefficients of piezoelectric films was constructed. A longitudinal vibration mode resonator with a hydrothermally synthesized (K,Na)NbO3 film deposited on a SrRuO3/SrTiO3 substrate was investigated. The fabricated vibrator consists of two upper electrodes, one for actuation and the other for sensing. A driving voltage was applied to the actuator electrode to generate mechanical vibration at its resonance frequency. The vibration velocity was measured with a laser Doppler vibrometer, and the output current from the shorted sensing electrode was also measured to simultaneously evaluate the inverse and direct piezoelectric responses. The obtained inverse piezoelectric coefficient e31̅ was −3.60 C/m2, while the direct piezoelectric coefficient e31̅ was almost same at −3.69 C/m2. From these values, the inverse and direct piezoelectric coefficients e31,f were −4.93 and −5.05 C/m2, respectively.