Simultaneous piezoelectric and ferroelectric characterization of thin films for MEMS actuators

The progress in lead zirconate titanate Pb(Zr_x,Ti_1-x)O₃ (PZT) thin film deposition and integration technology has led to an exponential growth of piezoelectric micro-electromechanical systems (piezo-MEMS), particularly for pure actuator devices such as inkjet print-heads and autofocus lenses. These devices rely on the transverse effective piezoelectric coefficient e_31,f in the converse mode. Thin film material development as well as quality monitoring during production require the measurement of dielectric, ferroelectric, and piezoelectric responses in a relevant way. We conceived and characterized a cheap, versatile, and easy to use setup, based on cantilever tip displacement detection and a charge amplifier allowing for simultaneous measurements of polarization and in-plane piezoelectric stress. The derivative of the obtained stress function gives directly e_31,f as a function of the electric field. In this work, data on unipolar excitation of sol-gel deposited PZT thin films are presented. The so derived, “active” e_31,f was found to be 40% larger than the value obtained from measurements of the direct effect (sensor mode).