PZT thin films for low voltage actuation: Fabrication and characterization of the transverse piezoelectric coefficient

Transverse piezoelectric coefficient d31 is a very important characteristic of lead zirconate titanate (PZT) thin films, which have great significance for enabling MEMS applications. In this work, the d31 characteristics of PZT thin-films actuated at low voltages of less than 1 V are investigated. Square-shaped bending-type PZT thin film microactuators comprising 600 nm thick sol-gel derived 52/48 PZT thin film on SiO2/Ta/Pt layers are fabricated using thin film deposition techniques and experimentally characterized for their piezoelectric behavior. Specifically, the characteristic of the in-plane transverse piezoelectric coefficient d31 is studied as a function of the PZT poling electric fields as well as the applied actuation voltages both at low voltages (<1 V) and high voltages (1-10 V). The d31 values of the PZT material are estimated via an experiment-model correlation where experimentally measured deflections and modal characteristics of the thin film actuator are corroborated with deflections and modal characteristics of the actuator in a finite element model. The results of the work presented show that d31 values of the PZT thin film material are considerably lower at low actuation voltages (<1 V) than at high actuation voltages (5-10 V) and that these values generally improve with the poling electric fields of the PZT sample. For the PZT thin films investigated in this work, a maximum effective d31 value for low actuation voltages was estimated to be −30 pC/N, and a maximum effective d31 value for higher actuation voltages that approach the coercive field of the PZT film was estimated to be −55 pC/N.