Improved Thin Film Piezoelectrics for Actuator Applications; Final process rept. 1 Apr-31 Dec 2007

摘要

Thin film piezoelectrics for microelectromechanical systems offer large motions, often with low hysteresis, high available energy densities, as well as high sensitivity sensors with wide dynamic ranges, and low power requirements. Among ferroelectric films, the majority of the MEMS sensors and actuators developed have utilized lead zirconate titanate (PZT) films as the transducer. Randomly oriented PZT films show piezoelectric e31 ,f coefficients of about - 6 to 7 C/m2 at the morphotropic phase boundary. It has recently been suggested that these coefficients are suppressed by Zr/Ti compositional gradients within the films. Consequently, the goal of this exploratory program was to prepare PZT films with different levels of compositional uniformity via chemical solution deposition, and quantify the resulting dielectric and piezoelectric constants of the films. Four different solution methods were examined. It was determined that published methods for reducing compositional gradients in PZT films were not straightforward to reproduce. Significantly better piezoelectric coefficients were obtained by using (001) oriented PbTi03 buffer layers to prepare (001) oriented PZT films. The net result is that it was possible to double the e31 ,f coefficient to -12 C/m2. The resulting thin films will enable lower voltage MEMS actuators as well as improved sensor and energy harvesting systems.