Ferroelectric property of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method
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Hitoshi Morioka and Hiroshi Funakubo Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama 226-8502, Japan
Nava Setter Ceramics Laboratory, Faculty of Engineering, Material Institute, Swiss Federal Institute of Technology (EPFL), CH-1015 Lausanne, Switzerland
Yasuo Cho Research Institute of Electrical Communication, Tohoku University, Miyagi 980-8577, Japan (Received 7 January 2004; accepted 25 March 2004)
Deposition of thin films via hydrothermal method has various advantages: low deposition temperature, high purity, deposition on a three-dimensional structure, and a large thickness. Although an epitaxial lead zirconate titanate (PZT) thin-film deposition has been reported, the ferroelectric measurement has not been conducted due to the peel-off morphology of the film. The current paper investigates the improvement of an epitaxial PZT thin film deposited via a hydrothermal method. By adjusting the position at which the substrate was suspended in the solution, smooth morphology surface was successfully obtained. As a bottom electrode, a 200-nm SrRuO3 thin film was deposited on SrTiO3 single crystals, and the PZT thin film was deposited on SrRuO3. The remanent polarization 2Pr and coercive electric field for PZT on SrRuO3/SrTiO3 (001) were 17.1 C/cm2 and 36 kV/cm, respectively, and those of PZT on SrRuO3/SrTiO3 (111) were 32.7 C/cm2 and 59 kV/cm, respectively. The reason for large imprint electrical field, 91 kV/cm and 40 kV/cm for each film, was unclear at this stage, although it is associated with self–alignment poling direction. This self–alignment poling direction was confirmed via scanning nonlinear dielectric microscopy and is thought to have been related to the deposition mechanisms.
I. INTRODUCTION
Epitaxial ferroelectric thin films, particularly lead zirconate titanate (PZT) epitaxial thin films, have intensively been studied for use in smart microelectrical mechanical systems (MEMS) and a ferroelectric random access memory (FeRAM) due to their large piezoelectric displacement and permanent polarization.1–3 Using a single-crystal substrate with a lattice constant close to that of PZT, the deposited film can be orientated according to the properties of the substrate. In an effort to obtain such a film, various film deposition processes have been explored, including sol-gel methods, sputtering methods, and chemical-vapor-deposition methods.4–6 However,
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0243 1862
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 6, Jun 2004 Downloaded: 12 Apr 2015
with these methods, a high-temperature crystallization process (above 600 °C) is required to achieve a PZT film. The advantage of the hydrothermal method is low reaction temperature, less than 200 °C. It is important to note that this temperature is below the Curie temperature of PZT and more than 400 °C below the reaction temperature required of other methods. Generally, a hightemperature procedure results in lead eva
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