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U2.2.1

GROWTH OF EPITAXIAL SITE-ENGINEERED Bi4Ti3O12-BASDED THIN FILMS BY MOCVD AND THEIR CHARACTERIZATION Hiroshi Funakubo, Tomohiro Sakai, Takayuki Watanabe, Minoru Osada1, Masato Kakihana2, Keisuke Saito3, Yuji Noguchi4 and Masaru Miyayama4 Department of Innovative and Engineered Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Kanagawa, Japan 1 PRESTO, Japan Science and Technology (JST), Kanagawa, Japan 2 Materials and Structures Laboratory, Tokyo Institute of Technology, Kanagawa, Japan 3 PANalytical Application Laboratory, Tokyo, Japan 4 Institute of Industrial Science, University of Tokyo, Tokyo, Japan ABSTRACT Thin films of BIT, La-substituted BIT (BLT) and La- and V-cosubstituted BIT(BLTV) were epitaxially grown on SrRuO3//SrTiO3 substrates at 850ºC by metalorganic chemical vapor deposition (MOCVD), and their electrical properties were systematically compared. All films on (100), (110) and (111)-oriented substrates were epitaxially grown with (001)-, (104)-/(014)and (118) –preferred orientations, respectively. The leakage current density of the BLTV film was almost the same with that of the BLT film, but was smaller than that of BIT film, suggesting that the La substitution contributed to the decrease of the leakage current density especially in pseudoperovskite layer. Spontaneous polarization of the BLTV film was estimated to be almost the same with the BLT film but was smaller that that of the BIT film. This is explained by the decrease of Tc with the La substitution, while V did not contribute to the change of the Curie temperature (Tc). On the other hand, the coercive field (Ec) value of the BLTV was smaller than that of the BIT and the BLT films. As a result, La substitution contributed to the decrease of the leakage current density together with the decrease of the spontaneous polarization due to the decrease of the Tc. On the other hand, V substitution contributes to the decrease of the defects that suppress the domain motion and increases the Ec value. Therefore, each substitution of La and V plays different roles and this contribution is remarkable for the films deposited at lower temperature.

INTRODUCTION Films of ferroelectric oxides have been widely investigated for the application not only the ferroelectric memory (FeRAM) but also the actuator and the microelectromechanical system (MEMS). Especially, series of bismuth layer-structured ferroelectrics (BLSFs), such as SrBi2(Ta,Nb)2O9 and (Bi,La)4Ti3O12 have been attracted as lead-free materials with a large ferroelectricity and good fatigue endurance against cyclic electric field. Problems of these materials are their high process temperature for a good ferroelectricity, e.g., above 650 oC for SrBi2Ta2O9 film. We developed the Bi4Ti3O12(BIT)-based novel materials having a large ferroelectricity even at low deposition temperature of 540 oC[1]. In the previous study, it was confirmed that Lanthanide and V cosubstitute for the Bi and Ti sites in pseudoperovskite layer in BIT structure

U2.2.2