Dynamic and long-time tests of the transverse piezoelectric coefficient in PZT thin films

A set up originally designed for e_31f measurements of piezoelectric thin films was operated in a way to assess life time issues with simultaneous recording of polarization change, PV-loop integral, and piezoelectric beam deflection. A 1μm thick PZT 53/47 thin film was subjected to 10⁹ unipolar pulses with 150 kV/cm driving voltage at 100 kHz and 50 % duty cycle. The observed fatigue was restricted to polarization change and leakage, and did not show up in the deflection. The ferroelectric loop recovered in a few minutes after stopping the voltage pulses. Further analysis suggests a heating of the element by the dissipated energy of the PV loop integral, becoming worse when leakage increases at higher temperatures. The critical piezoelectric stress was reasonably close to values derived from toughness coefficients of bulk PZT ceramics and for crack lengths corresponding to the film thickness.