Low Temperature Preparation of KNbO 3 Films by Hydrothermal Method and Their Characterization
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Low Temperature Preparation of KNbO3 Films by Hydrothermal Method and Their Characterization N. Kaneko1, T. Shiraishi1, M. Kurosawa2, T. Shimizu3 and H. Funakubo1 1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, J2-43, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan 2 Department of Information Processing, Tokyo Institute of Technology, G2-32, 4259 Nagatsutacho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan 3 Materials Research Center for Element Strategy, Tokyo Institute of Technology, S2-16, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan ABSTRACT KNbO3 films were prepared at 100 - 240oC on (100)cSrRuO3//(100)SrTiO3 substrates by hydrothermal method using KOH and Nb2O5 as source materials. The incubation time before starting deposition and the deposition rate after starting deposition increased and decreased with decreasing deposition temperature, respectively. Epitaxial {100}c-oriented KNbO3 films with 300 nm thick were successfully obtained at 100oC on (100)cSrRuO3//(100)SrTiO3 substrates for 144 h. We observed the typical butterfly-shape strain curves originated from the piezoelectricity for the first time for KNbO3 films deposited down to 120qC. INTRODUCTION The electronics devices fabricated on flexible organic substrates with piezoelectric functional layer such as sensors and displays have attracted great research interest [1-3] . In such heterostructure device assembly, piezoelectric functional layer must be deposited on organic substrate below 200oC due to the temperature limitation of the organic substrates. The piezoelectric materials deposited on the organic materials have been widely investigated for various applications[4-7]. Organic piezoelectric materials, such as Poly Vinilidene Fluoride (PVDF), prepared on organic substrates have been widely investigated[8-11]. However, the piezoelectricity of these organic materials is much smaller than that of the crystalline inorganic ones. To apply inorganic piezoelectric films on organic substrates, these films must be deposited below 200oC. However, deposition of all in-organics films require high deposition temperature above 600oC to achieve good quality crystalline piezoelectric films with good piezoelectric properties [12-17]. In hydrothermal method, inorganic films are deposited under high pressure precipitation chemical reactions. Therefore, this method makes it possible to prepare the crystalline inorganic films below 200oC[18-23]. In fact, BaTiO3 films were reported to be deposited on organic substrates below 200oC[24]. However, piezoelectricity of these films has not been reported. Moreover, BaTiO3 films were synthesized by the chemical reaction of BaOH solution and Ti metal coated on the organic substrate. Therefore it is difficult to grow thick film due to the diffusion limit of the Ti element in BaTiO3 film. In this study, we use KNbO3 as piezoelectric film. KNbO3 has good piezoelectric and electromechanical properties[25]. However, KNbO3 films were hardly deposited below 200oC.
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