Effect of Crystallographic Texture on Ferroelectric Performance of PZT Thin Films
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ABSTRACT A large set of films with textures ranging from almost fully random to highly {111 } textured were generated using an ULVAC ZX-1000 production sputter deposition machine. The PZT texture was altered by changing the I 1111 texture of the underlying Pt electrode, but the PZT thickness, composition, sputter deposition conditions, and crystallization anneals were held constant for all samples. X-ray diffraction peak intensities were used to calculate the volume fraction of {111}, {100}, and randomly oriented material composing the PZT films. All samples contained less than a 6% {100} textured volume fraction. It was found that the switchable polarization is linearly dependent on the {111 } textured volume fraction. The voltage required to achieve 90% saturation of the switchable polarization also has a linear dependence on the { 11 } textured volume fraction. The rate of fatigue and degradation of the switchable polarization caused by same-state and opposite-state retention tests were independent of the {111 } textured volume fraction. INTRODUCTION Because the spontaneous polarization of a ferroelectric is a first order tensor property that is directly determined by the ferroelectric crystal point group, it can be expected that the crystallographic texture of a polycrystalline ferroelectric thin film will influence the polarization switching performance. What is not immediately evident is whether variations in texture will
alter film performance for metrics that monitor changes in switchable polarization due to some environmental stress, e.g., number of switching cycles (fatigue) and temperature (retention). Although switchable polarization is the property monitored for metrics such as fatigue and retention, it cannot be assumed that the mechanisms underlying these phenomena are influenced by the crystallographic texture defining the measurable ferroelectric film polarization. This study provides insight into the effects of texture on switchable polarization and environment induced changes in the polarization for PbZr04 oTio600 3 (PZT) doped with Ca, Sr, and La [1]. In order to experimentally identify the direct relationship between texture and ferroelectric switching performance, it is necessary to determine the volume fraction of each type of texture within the ferroelectric film. The PZT prepared for this study contained two types of texture, viz., {100} and {1 11 }, in addition to randomly oriented volume fractions. The texture notation used here defines the PZT crystallographic planes lying parallel to the substrate surface. Integrated peak intensities from 0-20 X-ray diffraction measurements were used to determine the volume fractions foi each type of texture [2]. By comparing the experimentally measured volume fractions and the polarization switching performance metrics, the influence of texture on these metrics can be clearly observed.
205 Mat. Res. Soc. Syrup. Proc. Vol. 596 © 2000 Materials Research Society
EXPERIMENTAL PROCEDURE A series of PZT films with different crystallographic textures rang
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