Ion Modification for Improvement of Electrical Properties of Perovskite-based Ferroelectric Thin Films Fabricated by Che
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0902-T04-10.1
Ion Modification for Improvement of Electrical Properties of Perovskite-based Ferroelectric Thin Films Fabricated by Chemical Solution Deposition Method Hiroshi Uchida1, Shintaro Yasui1, Risako Ueno2, Hiroshi Nakaki1,2, Ken Nishida3, Minoru Osada4, Hiroshi Funakubo2, Takashi Katoda3 and Seiichiro Koda1 1 Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo, 102-8554, Japan 2 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8502, Japan 3 Department of Electronic and Photonic System Engineering, Kochi University of Technology, Kochi 782-8502, Japan 4 Advanced Materials Laboratory, National Institute of Materials Science (NIMS), Tsukuba 305-0044, Japan ABSTRACT Ion modification for various perovskite-based ferroelectric thin film using rare-earth cation was attempted for improving the electrical properties. Strategy for controlling the electrical properties is mainly based on two concepts, that is, (i) substituting the volatile cations such as Pb2+ and Bi3+, and (ii) controlling the crystal anisotropy of perovskite unit cell. In this study, the influences of ion-modification conditions (i.e., amount, species and occupying site of substituent cations) on the electrical properties of perovskite-based ferroelectric films fabricated by a chemical solution deposition were investigated. Substituting volatile cation in simple-perovskite oxides, such Pb2+ in Pb(Zr,Ti)O3 and Bi3+ in BiFeO3, for the rare-earth cations like La3+ and Nd3+ reduced the leakage current density of these films due to suppressing the metal and / or oxygen vacancies, as well as in layered-perovskite oxides, such as Bi4Ti3O12 films [i.e., strategy (i)]. Also, crystal anisotropy of perovskite-based oxides could controlled by varying the species and the occupying site of substituent cations [i.e., strategy (ii)]; for example, the crystal anisotropy of Pb(Zr,Ti)O3 lattice was elongated by Ti- and Zr-site (B-site) substitution using rare-earth cations whose ionic radii locate on the smaller part of rare-earth series (such as Y3+, Dy3+), that resulted in enhancing the spontaneous polarization from 20 to 25 µC/cm2. We concluded that the strategy for controlling the electrical property mentioned in this study would be applicable for a various kind of perovskite-based ferroelectric films. INTRODUCTION Active survey for novel ferroelectric materials with “Giant polarization”, i.e., larger spontaneous polarization than the conventional materials is proceeded frequently in recent researches because ferroelectric materials with excellent properties, i.e., large polarization, small coercive electric field, high electrical resistivity, etc., are required for manufacturing many electronic devices such as nonvolatile random access memories (NvRAMs), micro electro-mechanical systems (MEMS), piezoelectric sensors, etc. Some ferroelectric materials consisted of simple-perovskite crystal structure, including lead zirconate titanat
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