Dielectric Property Controls Using Crystal Structure Anisotropy in Bismuth Layer-Structured Dielectrics
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0902-T02-06.1
Dielectric Property Controls Using Crystal Structure Anisotropy In Bismuth Layer-Structured Dielectrics Muneyasu Suzuki1, Kenji Takahashi1, Takayuki Watanabe1,2, Tadashi Takenaka3 and Hiroshi Funakubo1,4 1
Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502, Japan 2 Institute of Solid State Research and CNI - Center of Nanoelectronic Systems for Information Technology, Research Center Juelich, 52425 Juelich, Germany 3 Department of Electrical and Engineering, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan 4 PRESTO, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan ABSTRACT Temperature dependency of the dielectric property of c-axis-oriented SrBi4Ti4O15 films was investigated in a temperature range from 80 to 400 K. c-axis-oriented epitaxial films with the film thickness of 30 and 140 nm were grown on (100)cSrRuO3//(100)SrTiO3 substrates by metal organic chemical vapor deposition (MOCVD). Increasing lattice distortions along the aand c-axes with decreasing film thickness was ascertained by XRD reciprocal space mapping. However, capacitance change normalized by the capacitance data at 300 K for with temperature was independent of the film thickness; it increased from 80 to 230 K and contrary decreased with increasing the temperature. Especially, the temperature coefficient of capacitance from 230 to 330 K was almost the same. It indicates that dielectric characteristics of these films for the temperature are independent of the film thickness in the actual use. Moreover, the same mesurement for the 120 nm-thick fiber-textured c-axis-oriented SrBi4Ti4O15 film deposited on the (100)cLaNiO3/(111)Pt/TiO2/SiO2/(100)Si substrate was also investigated. Resultant capacitance change with the temperature was basically the same with that of the epitaxial one, even though the temperature at maximum capacitance value was slightly shifted to lower temperature of 200 K. These data suggest that of capacitance change with the temperature was almost independent of the film thickness and the in-plane orientation.
INTRODUCTION Thin film of the dielectric material with high dielectric constant (εr) beyond 200 is essential for the development of the electric devices such as dynamic random access memory. However, the degradation of the εr with decreasing the film thickness is widely reported for the thin film of the perovskite type oxide [1-4]. This prevents the development of the high density capacitor. To solve this problem, a novel candidate of series of a material is proposed by our groups [5]. It is the bismuth layer-structured dielectrics along the c-axis direction, the structure of which has a stack of the bismuth oxide layer and the pseudo perovskite layer. We already
0902-T02-06.2
ascertained no degradation of the εr with decreasing film thickness for the c-axis oriented SrBi2Ta2O9 film. This material is widely known as a ferroelectric material for the nonvolatile ferroelectric random access memory (N
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