Electromechanical properties and domain-related effects in ferroelectric thin films

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Abstract
The possibility of miniaturization and integration with silicon technology makes ferroelectric films promising for micro sensors and micro actuators. Despite the increasing range of applications, the electromechanical properties of thin-layer ferroelectrics are poorly understood as compared to those of bulk materials. In particular, it is an open question whether the non-180° domain motion, which determines the strain response in ferroelectric ceramics, contributes to electric field-induced strain in thin films. This paper reviews author's recent investigations on electromechanical properties of ferroelectric thin films, with special emphasis on domain-related effects. The materials list includes Pb(Zr,Ti)O3 (PZT), Pb(Ca,Ti)O3 (PCT) and SrBi2Ta209 (SBT). It is shown that in some cases the non-180° domain wall contribution is necessary to describe the mechanical strain under sufficiently high electric field. This contribution is found to be important for PZT films of the morphotropic phase boundary and rhombohedral compositions. In PCT films the strain response as a function of Ca content is explained based on the reorientation of 90° domains. In SBT films pure electrostrictive relationship is found between the strain and polarization suggesting that the non-180° domains are either absent or inactive in this material.