The Effects of Film Thickness and Texture on the high and Low-Field stress Response of Lead Zirconate Titanate Thin Films

Lead zirconate titanate (PZT) thin films are currently employed in non-volatile ferroelectric memories (FRAM's) and are intended to be used as the active material in a number of microelectromechanical systems (MEMS). Several groups have reported that both the piezoelectric and dielectric characteristics of ferroelectric thin films improve with an increase of film thickness, though the reasons for those improvements are unclear. Previous investigations on the effects of biaxial mechanical stress indicate that non-180° domain wall motion is limited in PZT 52/48 films less than 0.5 μm thick. It is possible that some of the improvements of the dielectric and piezoelectric characteristics reported for thicker films (i.e. films thicker than 0.5 μm) are associated with an increase of extrinsic contributions to the properties. To evaluate domain wall mobility in thicker films, the high and low-field stress response of sol-gel PZT fabricated with either rapid thermal processing or conventional furnace annealing were investigated. Films with thicknesses ranging from 0.6 to 5.0 μm thick were measured as a function of applied biaxial stress (±110 MPa). It was found that for all films tested the changes of capacitance were on the order of 2–3%. High-field measurements showed: (1) the coercive field to be insensitive to applied stress, (2) remanent polarizations to decrease about 20% at the maximum applied tension, (3) remanent polarizations to increase less than 10% with applied compression, and (4) all changes to be reversible over the stress range investigated. These results suggest that extrinsic contributions are limited for the films tested.