Preparation and Characterization of a- and b-Axis-Oriented Epitaxially Grown Bi 4 Ti 3 O 12 -Based Thin Films on Rutile-
- PDF / 115,246 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 70 Downloads / 184 Views
Preparation and Characterization of a- and b-Axis-Oriented Epitaxially Grown Bi4Ti3O12-Based Thin Films on Rutile-Type Oxides Takayuki Watanabe, Keisuke Saito1, Minoru Osada2, and Hiroshi Funakubo Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan 1 Application Laboratory, Analytical Department, Philips Japan, Ltd., 35-1 Sagamiono 7-chome, Sagamihara-shi, Kanagawa 228-0803, Japan 2 Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan ABSTRACT a- and b-axis-oriented epitaxial Bi4Ti3O12 films were prepared on (101)TiO2 substrates (rutile) at 600˚C by metalorganic chemical vapor deposition (MOCVD). Subsequently, the same films were similarly prepared on (101)-oriented conductive materials with the same rutile structure and similar lattice parameters as TiO2, such as RuO2 and IrO2. Their perfect epitaxial growth was confirmed by several X-ray diffraction measurements. RuO2 and IrO2 were deposited on not only structurally equivalent (101)RuO2//(101)TiO2 and (101)IrO2//(101)TiO2 structures, but were also successfully deposited on the corundum (012)Al2O3 and (110)Al2O3 single crystals by the MOCVD and rf-sputtering method, respectively. A well-saturated P-E hysteresis with a remanent polarization above 20 µC/cm2 was observed for a- and b-axis-oriented Bi4Ti3O12-based materials, (Bi4-xNdx)(Ti3-yVy)O12 (BNTV), that were epitaxially grown on rutile-rutile and rutile-corundum stacking structures. These results should enable broader application of the bismuth layer-structured ferroelectrics. INTRODUCTION Bismuth layer-structured ferroelectrics (BLSFs), generally described as (Bi2O2)2+(Am-1BmO3m+1)2- (m=1-5), have been investigated for ferroelectric random access memory (FeRAM), piezoelectric and optical switching devices because of their fatigue-free properties, large piezoelectric coefficient and optical anisotropy [1-3]. Up to now, the dependence of the ferroelectricity on the film orientation and the m-number were systematically investigated using various kinds of epitaxially grown BLSF films [4-6]. However, the characterization of the ferroelectricity along the [100] direction, the polar axis with the largest polarity, is limited only to bulk single crystals or thicker films (>10µm) peeled from the substrate [7,8], even though there are several reports of epitaxially grown BLSF films deposited on single crystal substrates such as (110)MgO and (110)MgAl2O4 [9,10]. This is because a suitable bottom electrode which overcomes the difficulty of the in-plane long-range lattice matching with the long c-axis, which is peculiar to BLSFs, has not been proposed. J. Lettieri et al. and H.N. Lee et al. have shown that epitaxial BLSFs can be grown on non-(100) perovskites either coated with epitaxial SrRuO3 as the bottom electrode, or using doped SrTiO3 substrates, and their electrical properties were evaluated. This has allowed a good deduction of film properties along [100], even though t
Data Loading...
