Texture control in lead zirconate titanate multilayer thin films

Multilayer actuators (MLAs) offer an increase of force per unit area, a reduction in power consumption, and a reduction in required driving voltages compared with singlelayer actuators. For example, switching from a single 0.5- or 1.0-μm layer of PZT to multiple 250-nm-thick layers would enable a 2/3 to 3/4 reduction in actuation voltage and an increase of 2 to 3 times in actuation force per area for a PZT MEMS switches and robotics. Efforts have been focused on developing actuators using four 250-nm-thick layers of PZT with a Zr/Ti ratio of 52/48 (i.e., the morphotropic phase boundary). The PZT films used a previously established method of achieving greater than 98% (001/100) oriented PZT by chemical solution deposition (CSD). By performing X-ray diffraction measurements between each layer, the texture within the films could be monitored during the growth process. To electrically measure the quality of the PZT multilayer stack, a series of six-sided capacitors were fabricated. The devices were connected in parallel with an average dielectric constant of 1150 for each PZT layer and an average total capacitance of 45 nF. In addition to capacitors, cantilever actuators were fabricated to measure the piezoelectric induced deformation. Comparisons with 100-μm-long cantilever between a single 1-μm-thick PZT and four 250-nm-thick layer PZT stack have shown comparable displacements of |3.7| μm and |4.0| μm, respectively, with an applied electric field of 10 V/μm across the film. These measurements on MLA PZT films demonstrate high piezoelectric coefficients that are suitable for tactile radio and milimeterscale robotic devices.