Characterization of Ferroelectric Property of c-axis and non-c-axis Oriented Epitaxially Grown Bismuth Layer-Structured
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Characterization of Ferroelectric Property of c-axis and non-c-axis Oriented Epitaxially Grown Bismuth Layer-Structured Ferroelectric Thin Films with Different m-numbers Prepared by MOCVD Takayuki Watanabe, Tomohiro Sakai, Atsushi Saiki1, Keisuke Saito2, Toyohiko Chikyo3, and Hiroshi Funakubo Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama-shi, Kanagawa 226-8502, Japan 1 Research Cooperation Section, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8550, Japan 2 Application Laboratory, Analytical Department, Philips Japan, Ltd., 35-1 Sagamiono 7-chome, Sagamihara-shi, Kanagawa 228-0803, Japan 3 National Research Institute for Metals, Tsukuba Laboratory, 1-2-1 Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan
ABSTRACT Epitaxial thin films of bismuth layer-structured ferroelectrics (BLSF) with different m-numbers, i.e., Bi2VO5.5 (BVO) (m=1), SrBi2Ta2O9 (SBT) (m=2), and Bi4Ti3O12 (BIT) (m=3), were grown by metalorganic chemical vapor deposition (MOCVD). (00l)-oriented films were deposited on (100)SrTiO3. (114)-oriented BVO, (116)-oriented SBT, and (118)-oriented BIT films were deposited on (110)SrTiO3. Moreover, (102)-oriented BVO, (103)-oriented SBT, and (104)-oriented BIT films were deposited on (111)SrTiO3. On (100), (110), and (111)SrTiO3 substrates, c-axis of the deposited films was tilted about 0Û, 45Û, and 56Û, respectively, against perpendicular to the surface of the substrates irrespective of m-number. This suggests the growth of crystallographic equivalent orientation. The distinctive surface morphology originated to the feature of the film orientation was observed. The dielectric constant and the leakage current of c-axis-oriented film was smaller than that of non-c-axis-oriented one, indicating smaller dielectric constant and leakage current along c-axis than a- or b-axes. A larger ferroelectric anisotropy was ascertained for SBT and BIT films. Furthermore, the evaluated spontaneous polarization along a- and c- axes of BIT from the data of the epitaxially grown BIT films well agreed with the reported one for the single crystal. This suggests the ferroelectric property was not strongly affected by the strain in the films.
INTRODUCTION Thin films of bismuth layer-structured ferroelectrics (BLSF) have been investigated for a ferroelectric random access memory (FeRAM) application because of its good ferroelectric properties, especially high fatigue endurance. We have already reported that the epitaxially grown SrBi2Ta2O9 (SBT) and Bi4Ti3O12 (BIT) films have high fatigue endurance [1, 2]. However, BLSF thin films with different m-number have not been systematically investigated. The understanding of the common feature of BLSF is essential to find out suitable BLSF material for FeRAM applications. In this study, epitaxial Bi2VO5.5 (BVO) (m=1), SBT (m=2), and BIT (m=3) films with c- and non-c-axis-orientations were systematically grown and characterized to find out the common feature of crystal growth and the electrical pro
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