Formation of c-Axis-Oriented Bi4Ti3O12 Films with Extremely Flat Surface by Spin-Coating

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Abstract
The formation of c-axis-oriented Bi4Ti3O12 (BIT) films by spin-coating has been investigated. The crystallinity of BIT films depends on the Bi to Ti molar ratio of the starting BIT solution and on the annealing temperature. The BIT film spin-coated with a 10% Bi-rich solution and annealed at 850° C shows a highly c-axis-oriented crystallinity. In addition, it is found that a BIT layer spin-coated on this c-axis-oriented film becomes highly c-axis-oriented even if the starting solution is not Bi-rich, and that the obtained film has an extremely flat surface when the first BIT layer is thinly applied. The resulting films exhibit good properties for use in metal-ferroelectric-metal-insulator-semiconductor (MFMIS) structural memory devices, such as a low leakage current density of 7×10-7 A/cm2 at 3 V, a remanent polarization of 2.5 µ C/cm2, a coercive field of 8 kV/cm, and a dielectric constant of 120.