Crystal structure and dielectric property of epitaxially grown (Ba, Sr)TiO 3 thin film prepared by molecular chemical va
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Crystal structure and dielectric property of epitaxially grown (Ba, Sr)TiO3 thin film prepared by molecular chemical vapor deposition Hiroshi Funakubo Department of Inovative and Engineering Materials, Interdisciplinary Graduated School of Science and Engineering, Tokyo Institute of Technology, 4259, Nagtsuda-cho, Midori-ku, Yokohama, 226 Japan
Yutaka Takeshima Functional Materials Research Development, R & D Group, Murata Mag. Co. Ltd., Yasu-gun, Siga, 520-23, Japan
Daisuke Nagano, Kazuo Shinozaki, and Nobuyasu Mizutani Department of Inorganic Materials, Faculty of Engineering, Tokyo Institute of Technology, 2-12-1, Meguro-ku, O-okayama, Tokyo, 152, Japan (Received 26 July 1997; accepted 25 November 1997)
Epitaxially grown (Ba, Sr)TiO3 thin films were prepared on (100)MgO and (100)Pt k (100)MgO substrates by molecular chemical vapor deposition (MOCVD). The lattice parameter increased with increasing Bay(Ba 1 Sr) ratio in the film and was higher than the reported value for bulk (Ba, Sr)TiO3 . The dielectric constant at room temperature reached the maximum value at a lower Bay(Ba 1 Sr) ratio compared to the reported one for bulk (Ba, Sr)TiO3 . The temperature showing the maximum dielectric constant was higher than the reported value for bulk (Ba, Sr)TiO3 . These results can be explained by the compressive stress applied to the film under the cooling process after the deposition.
I. INTRODUCTION
(Ba, Sr)TiO3 film is a promising high dielectric constant material for use in the capacitor of dynamic random access memory (DRAM) because of its high dielectric constant and low leak voltage properties.1 Many researchers pointed out that the crystal structure and the electrical property of the film were different from that of the reported ones for the sintered body. For example, an abnormal large lattice parameter was reported by some researchers for (Ba, Sr)TiO3 film deposited by the sputtering method.2,3 These are considered to originate in the residual strain in the film. Therefore, it is essential to investigate the effects of the stress applied to the film on the crystal structure and the electrical property by using epitaxially grown (Ba, Sr)TiO3 film. CVD has the advantage of making high quality film, especially epitaxially–grown film, because of the absence of high energy particles during deposition. However, most of the research on (Ba, Sr)TiO3 film prepared by CVD has mainly been focused on the measurement of electrical properties of the film with less than 100 nm in thickness for application to the capacitor of DRAM.4–7 Therefore, investigation of the effect of the applied stress has seldom been reported for the film prepared by CVD. We have studied the preparation of epitaxially grown PbTiO3 ,8 Pb(Zr, Ti)O3 ,9 (Pb, La) (Zr, Ti)O3 ,10 BaTiO3 , and SrTiO3 11 films by CVD and the effect of the applied stress on the crystal structure. In the present study, we prepared epitaxially grown (Ba, Sr)TiO3 films on (100)3512
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