Influence of texture on the switching behavior of Pb(Zr 0.70 Ti 0.30 )O 3 sol-gel derived thin films
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Influence of texture on the switching behavior of Pb(Zr0.70 Ti0.30 )O3 sol-gel derived thin films Keith G. Brooks, Radosveta D. Klissurska, Pedro Moeckli, and N. Setter Laboratoire de C´eramique, Ecole Polytechnic F´ed´erale de Lausanne, Lausanne, Switzerland (Received 1 August 1995; accepted 22 August 1996)
Rhombohedral Pb(Zr0.70 Ti0.30 )O3 thin films of four different well-defined textures, namely, (100), (111), bimodal (110)y(111), and (100)y(111), were prepared by a sol-gel method. The films were characterized in terms of grain size, presence of second phases, surface roughness, columnarity of grains, and other microstructural features. The dielectric, ferroelectric, and fatigue properties were investigated, with emphasis on the hysteresis switching characteristics. Results are discussed from the reference point of the allowable spontaneous polarization directions available for the different textures. The values of coercive field, remanent and saturation polarization, and slope of the loop at the coercive field, at saturating fields can be qualitatively explained based on the texture, independent of microstructural differences. The occurrence of surface pyrochlore, however, is observed to affect the functionality of the saturation curves, particularly for the samples of bimodal texture. Shearing of the hysteresis curves of the bimodal films is also attributed to surface microstructural features. The occurrence of nonswitching 71± or 109± domains in the (111) and (110)y(111) textured films is hypothesized based on a comparison with the data from the (100) textured film. Corrected saturation polarization values agree with the spontaneous polarization values of rhombohedral PZT single crystals and published calculated values for rhombohedral PZT ceramics. The fatigue characteristics show increases in the switching component of polarization in the range 103 –107 bipolar cycles, particularly for the (111) textured sample. Onset of fatigue is observed for all samples between 107 and 108 switching cycles.
I. INTRODUCTION
Pb(Zr12x Tix )O3 thin films have been studied intensively during the past decade for nonvolatile ferroelectric memory applications.1 A majority of the investigations have centered around compositions in close proximity to the rhombohedral/tetragonal morphotropic boundary at x ø 0.47.2 The morphotropic composition and those to the tetragonal side of it sx . 0.47d are interesting, as maximum values of remnant polarization sPr d are observed.3–6 Softer hysteresis with lower Pr and coercive field sEc d occurs for rhombohedral compositions sx , 0.47d.2–4,6–8 Rhombohedral compositions thus have the advantage of lower switching fields.3 In the preparation of PZT thin films by various deposition techniques, it has been reported that the ease of nucleation of the perovskite structure improves with Ti addition. Typically in rhombohedral (Zr-rich) films, rosette-type microstructures are observed (particularly for sol-gel derived films) due to the higher perovskite
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