Tunability and sensitivity modification by poling on PZT film of frequency-tunable ultrasonic microsensors

Piezoelectric diaphragm-type tunable ultrasonic microsensors have been investigated in their performance modification induced by poling on the piezoelectric/ferroelectric thin film on the sensor diaphragm. The tunable sensor has a tuning electrode besides a sensing electrode to tune the resonant frequency through converse-piezoelectric stress in the diaphragm. Tunability and sensitivity changes has been traced under voltage applications on the tuning and poling electrodes on sensors having flat and buckled diaphragms. The buckled-diaphragm sensors have shown anomalies that the sensitivity decreases at a high poling voltage region and sensitivity butterfly curve to the tuning voltage reverses upside down in the voltage range. The buckling deflection shape of the diaphragm has been profiled under the poling and tuning voltage applications, and the origin of the sensitivity anomalies have been concluded to be a buckling direction reversal in the sensing electrode part induced by the combination of the poling and tuning stress.