Ferroelectric Domain Structure and Local Piezoelectric Properties of Sol-Gel Derived Pb(Zr 1-x Ti x )O 3 Films
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Ferroelectric Domain Structure and Local Piezoelectric Properties of Sol-Gel Derived Pb(Zr1-xTix)O3 Films I. K. Bdikin, V. V. Shvartsman, A. L. Kholkin, Seung-Hyun Kim* Department of Ceramics and Glass Engineering/CICECO, University of Aveiro, 3810-193 Aveiro, Portugal * INOSTEK Inc., Gyeonggi Technopark, 1271-11 Sa 1, Sangnok, Ansan, Gyeonggi 425-791, Korea ABSTRACT High-resolution domain studies are performed on Pb(Zr1-xTix)O3 (PZT) films of different thicknesses and compositions (x=0.30, 0.48, and 0.70) by piezoresponse force microscopy (PFM). Depending on the composition, the orientation of the films is varied from purely (111) (related to the orientation of Pt bottom electrode) to a more random texture. Statistical processing of the obtained domain images is used to analyze the correlation between the composition of the films and their nanoscale piezoelectric properties. It is shown that the virgin (unpoled) films possess large piezoelectric activity comparable to that after local poling (self-polarization effect). This corresponds to a clear predominance of the domains with polarization oriented from the free surface of the film to the bottom electrode. Both the average piezoelectric signal and half-width of the piezoelectric histograms depend on the composition and thickness of the films. The largest local piezoelectric coefficient and the broadest distribution are found for tetragonal (x=0.70) films with almost pure (111) texture. The results are discussed in terms of texture and PFM instrumentation effects on local piezoelectric measurements. INTRODUCTION Lead zirconate titanate Pb(Zr1-xTix)O3 (PZT) has been extensively studied over last thirty years because of its excellent ferroelectric, dielectric and piezoelectric properties. Many potential applications are now foreseen for PZT thin and thick films such as nonvolatile memory cells and microelectromechanical devices. PZT experiences a rhombohedral-to-tetragonal phase transition as a function of x, where material exhibits exceptionally high dielectric and piezoelectric properties near the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases. Recently, a new monoclinic phase has been observed in PZT at x∼0.5 [1, 2] that stimulated a new wave of interest to this technologically important material. It is known that the properties of ferroelectric thin films are greatly influenced by their thickness and texture. Therefore, an immense amount of studies has been dedicated to the thickness, composition and texture effects on the electrical properties (see, e.g., references [3-6]). Since the size of thin film devices is expected to approach sub-µm range, the local techniques to study their properties are becoming increasingly important. One of these techniques, piezoresponse force microscopy (PFM), has been successfully used to investigate the physical properties of ferroelectrics at the scale limited by only the size of the PFM tip (∼10 nm). In this work, local piezoelectric characteristics of commercially available PZT films are
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