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In ferroelectric thin films for capacitive and piezoelectric applications, it is important to understand which mechanisms contribute to the observed dielectric constant and piezoelectricity. In soft PZT (PbZr1−xTixO3) ceramics, over half the room temperature response is associated with domain wall contributions to the properties. However, recent studies on bulk ceramics have demonstrated that the number of domain variants within grains, and the mobility of the twin walls depend on the grain size. This leads to a degradation in the dielectric and piezoelectric properties for grain sizes below a micron. This has significant consequences for thin films since a lateral grain size of 1 μm is often the upper limit on the observed grain size. In addition, since the pertinent domain walls are ferroelastic, the stress imposed on the film by the substrate could also clamp the piezoelectric response. To investigate these factors, controlled stress levels were imposed on PZT films of different thickness while the dielectric and electromechanical properties were measured. It was found that for undoped sol-gel PZT 40/60, 52/48, and 60/40 thin films under a micron in thickness, the extrinsic contributions to the dielectric and electromechanical properties make very modest contributions to the film response. No significant enhancement in the properties was observed even when the film was brought through the zero global stress condition. Comparable results were obtained from laser ablated films grown from hard and soft PZT targets. Finally, little twin wall mobility was observed in AFM experiments. The consequences of this in terms of the achievable properties in PZT films will be presented. Work on circumventing these limitations via utilization of antiferroelectric phase switching films and relaxor ferroelectric single crystal films will also be discussed.

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Lead zirconate titanate thin films offer considerably larger piezoelectric coefficients than do ZnO, and so are attractive for microelectromechanical sensors and actuators. To date, much of the research in this field has concentrated on undoped PZT. In this work, PZT films grown from both hard and soft PZT targets have been deposited on platinum coated silicon wafers by pulsed laser deposition so that the effect of doping on the properties can be determined. Dielectric constants of 1000–1500 are regularly achieved in both types of films, with loss values varying from 0.01 for soft films to 0.03 for hard films. Remanent polarizations are typically 30 μC/cm2 for both types of films with no observable difference in coercive fields. When subjected to ∼140 MPa of biaxial tension and compression, only small (∼5%) reversible changes were observed, indicating a lack of substantial domain reorientation in the films.