Nanoscale Piezoelectric Phenomena in Epitaxial PZT Thin Films
This chapter reviews nanoscale piezoelectric phenomena in epitaxial lead zirconate titanate (PZT) ferroelectric thin films The first part of the paper focuses on theoretical predictions of the field dependent piezoelectric behavior of bulk single crystal
- PDF / 3,208,872 Bytes
- 29 Pages / 439.37 x 666.142 pts Page_size
- 44 Downloads / 247 Views
V. Nagaraj an , A. Roytburd, and R. Ramesh This chapter reviews nanoscale piezoelectric phenomena in epitaxial lead zirconate titanate (PZT) ferroelectric thin films. The first part of the paper focuses on theoretical predictions of the field dependent piezoelectric behavior of bulk single crystal and thin film PbZrxTi 1_x0 3. A Ginzburg-Landau-Devonshire-type phenomenological thermodynamic theory for tetragonal single domain PZT is employed to explain the electric field dependence of piezoelectric properties. It demonstrates the presence of a strong non-linearity of converse piezoelectric coefficient under large external electric field in both bulk crystal and epitaxial tetragonal PZT thin films. The results of the model are used to interpret piezoelectric responses of model epitaxial thin films and nanostructures using voltage modulated scanning force microscopy. They are presented with particular focus on the longitudinal piezoelectric constant d33 in nanoscale capacitors (or islands) of various PZT compositions. An effective stress model is presented to explain the dependence of d 33 on the lateral size. We show that by altering the electromechanical interplay between the substrate and the ferroelectric thin film an unusual field dependence of the d33 exists in compositions closer to the morphotrophic phase boundary. Due to this effect, the change in strain at saturation field is twice the theoretical prediction, opening up possibilities such as highly strain tunable devices. Finally we discuss in highly tetragonal PbZro.2Tio.803, movement of elastic 90° domains with applied DC field, a phenomenon hitherto observed only in bulk single crystals or ceramics. This results in a d 33 of - 250 pm/Vat remanence, which is approximately 3-4 times the predicted value of 87 pm/V for a single domain single crystal.
6.1 Introduction Ferroelectric materials, which display large electromechanical interactions, have been used for many years in sensors, actuators and transducers. While most commercial electromechanical materials are based on linear piezoelectric mechanisms, nonlinear electromechanical interactions are gaining interest in engineering structures with tunable properties [1]. Therefore in recent years, piezoelectric nonlinearity has been a key issue in the development of high performance electromechanical devices. As a consequence much attention has been paid to the modeling of the nonlinear behavior under high fields. Numerous treatises of the piezoelectric coefficient field dependence have been proposed either starting from the free M. Alexe et al. (eds.), Nanoscale Characterisation of Ferroelectric Materials © Springer-Verlag Berlin Heidelberg 2004
164
V. Nagarajan, A. Roytburd, and R. Ramesh
energy equation and using field polynomial expansions [2,3] or introducing empirical bias and amplitude dependence [4] without any thermodynamical considerations. In this paper, we present a phenomenological thermodynamic approach to study the nonlinear electric field dependence of dielectric and piezoelectric properti
Data Loading...
