Strain and Grain Size Effects on Epitaxial PZT Thin Films

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Strain and Grain Size Effects on Epitaxial PZT Thin Films Oscar Blanco and Jesus Heiras1 Centro de Investigación en Materiales, DIP-CUCEI, Univ. de Guadalajara Apdo. Postal 2-638, CP. 44281, Guadalajara, Jal., México 1 Centro de Ciencias de la Materia Condensada, UNAM Apdo. Postal 2681, C.P. 22800, Ensenada, B.C., México ABSTRACT Epitaxial ferroelectric thin films of lead zirconium-titanium oxide, Pb(Zr0.53Ti0.47)O3 (PZT), were successfully grown on SrTiO3, LaAlO3, and Sr(Nb)TiO3 single crystal substrates by a modified RF sputtering technique at high oxygen pressures. The structural properties of the films were evaluated by θ/2θ, ω and φ scans. From these data the crystalline orientation relationships may be extracted. For films grown on SrTiO3 and Sr(Nb)TiO3 substrates, the following orientation relationships were determined: PZT [001] parallel to [001] of the substrate, and PZT [100] parallel to [100] of the substrate. Films grown on LaAlO3 substrates showed a bi-domain crystalline structure with orientation relationships as follows: PZT [100] parallel to [001] of the substrate and PZT [001] parallel to [001] of the substrate. This work was focused to the determination the strain and grain size coefficients, and the analysis of their contribution on the peak broadening in the XRD patterns, and in considering their effects over the ferroelectric behavior. From Williamson-Hall plots, it was possible to conclude that the enhancement of the crystalline film properties (epitaxy and single crystalline domains) reduce the short range strains contribution to peak broadening. On other hand, the grain size contribution to peak broadening was increased with the enhancement of the film cristallinity. INTRODUCTION Thin films of several ferroelectric materials have been studied by their potential use in numerous applications. Such applications included devices in the nano-scale sizes, for example, FRAM´s, NVRAM´s and electro-optical devices [1,2,3]. In this way, many research efforts are dedicated to studying and understanding the deviations from the bulk properties observed in thin films resulting from the lattice mismatch strain and the size effects (film thickness and grain size). In particular, epitaxial films deposited on lattice-mismatched substrates are often subject to the large coherence strain [4]. In these films, the broadening (FWHM) of the diffractions peaks is the sum of contributions from the grain (domains) size and the local strain. In this work, we studied the strain and grain size effects on the structural characteristics and ferroelectrics properties of the films. EXPERIMENTAL DETAILS Epitaxial ferroelectric thin films of lead zirconium-titanium oxide, Pb(Zr0.53Ti0.47)O3 (PZT), were RF sputtered onto SrTiO3 (STO), LaAlO3 (LAO), and Sr(Nb)TiO3 (SNTO) single crystal

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substrates by a modified RF sputtering technique at high oxygen pressures as reported previously [5,6]. The relevant deposition conditions are summarized in the Table I. The crystalline quality and structure features were eval