Annealing effect on in-plane alignment and surface morphology of epitaxial Bi 4 Ti 3 O 12 thin films prepared by the che
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Y. Park Department of Dental Materials & Dental Materials Research Institute, School of Dentistry, Chonnam National University, 5 Hak 1 dong, Dong-gu, Kwangju 501-190, Republic of Korea (Received 8 January 2001; accepted 12 June 2001)
Bi4Ti3O12 thin films were grown epitaxially on SrTiO3(100) substrates by chemical solution deposition using metal naphthenates as starting materials. Homogeneous Bi–Ti solution with toluene was spin-coated onto the substrates and pyrolyzed at 500 °C for 10 min in air. Highly c-axis-oriented Bi4Ti3O12 thin films were crystallized by annealing pyrolyzed films at 艌650 °C. The x-ray pole-figure analysis indicated that the Bi4Ti3O12 thin films have an epitaxial relationship with the SrTiO3(100) substrates. The surface morphology of the films annealed at lower temperature, i.e., 650 °C, exhibited flat and smooth surfaces, while films annealed at higher temperatures, i.e., 750 and 800 °C, were characterized by three-dimensional outgrowth. I. INTRODUCTION
Among the various ferroelectric materials, bismuth titanate (Bi4Ti3O12, BIT) with a bismuth layer structure exhibits good ferroelectric properties and fatigue durability. BIT has a spontaneous polarization in the a–c plane at an angle of about 45° to the a axis and exhibits two independently reversible components along the c and a axes. BIT crystals show strong anisotropic properties and have a low coercive field value and a dielectric constant of 3.5 kV/cm and 130, respectively, along the c axis.1,2 Thus, BIT has been widely investigated for nonvolatile memories, due to its low coercive field, small dielectric constant, and high Curie temperature.3–5 Owing to the small coercive field along the c axis, c-axisoriented BIT thin films are expected to be used for electronic memory devices requiring a low drive power. However, in comparison of perovskite-related materials such as BaTiO3 and Pb(Zr,Ti)O3 with cube on cube structured films, the surface morphology of BIT films has generally less homogeneity because of its orthorhombic structure. Thus, it is very difficult to prepare highdensity devices. Knowledge of surface morphology and roughness for the film is very important for the applications of electrical and optical devices, since atomically smooth film surfaces are required to obtain sharp interfaces and reduce interface resistance in heterostructure devices. Thus, it is clear that crystalline quality and surface smoothness is required for fabricating devices with high performance. Randomly oriented grain and coarsegrained surfaces result in nonuniform device functions. J. Mater. Res., Vol. 16, No. 9, Sep 2001
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Recently, the fabrication of highly c-axis-oriented BIT thin films has been achieved by several methods such as metalorganic chemical vapor deposition,6 pulsed laser deposition (PLD),7 and laser molecular beam epitaxy.8 Chemical solution deposition (CSD) has been successfully used to prepare c-axis-oriented BIT films.9 We already reported the epitaxial growth of BIT films on L
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