Simultaneous piezoelectric and ferroelectric characterization of thin films for MEMS actuators

The progress in lead zirconate titanate Pb(Zr-x,Ti1-x)O-3 (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 inplane 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).