Compensation of Thermal Effects in PZT and Sc_0.2Al_0.8N PMUTs Through DC Bias Tuning

In this work, we present a comparison study on the effects of thermal expansion induced deformation and resonance frequency drift in physical vapor deposition (PVD) lead-zirconate-titanate (PZT) and Sc0.2Al0.8N (ScAlN) piezoelectric micromachined ultrasonic transducers (PMUTs). The membrane deformation and resonance frequency of a PZT-PMUT and a ScAlN PMUT, which have same design except the piezoelectric layers, were thoroughly measured with various stress condition induced by direct current (DC) bias voltage. Finally, the experiment results led us to propose a method for temperature compensation utilizing DC bias. This approach effectively reduces the frequency variation by 10-fold and ${{\text{k}}_{\text{t}}}^2$ variation within 0.6% for PZT PMUT across the temperature range of 25-100°C. The same proposed method further reduces the frequency variation of thermal effects on ScAlN PMUT by 2-fold.