Crystal structure and dielectric property of bismuth layer-structured dielectric films with c-axis preferential crystal orientation

Thin films of bismuth layer-structured dielectrics (BLSDs), CaBi4Ti4O15, and SrBi4Ti4O15, were prepared by a chemical solution deposition (CSD) technique on various substrates, such as (111)Pt/TiO₂/(100)Si, (100)LaNiO ₃/(111)Pt/TiO₂/(100)Si, and (100)SrRuO₃//(100) SrTiO₃ substrates. Conductive perovskite oxide LaNiO₃ with (100) preferential crystal orientation was introduced into the interface between the BLSD film and the (111)Pt/TiO₂/(100)Si substrate to control the crystal orientation of BLSD by lattice matching between pseudo-perovskite blocks in the BLSD crystal and the (100)LaNiO₃ plane with the perovskite structure. The (00/) planes of BLSD crystals were preferentially oriented on the substrate surface of the (100)LaNiO ₃/(111)Pt/TiO₂/(100)Si, whereas randomly-oriented BLSD crystals with lower crystallinity were only obtained on the surface of (111)Pt/TiO₂/(100)Si substrate. The (001)-oriented BLSD films exhibited the leakage current densities below 10^-7A/cm² at ±50 kV/cm, which is significantly lower than those for randomly-oriented films, above 10^-6 A/cm², The room-temperature dielectric constants (ε_r)p of CaBi₄Ti₄O₁₅ and SrBi₄Ti₄O₁₅ thin films on the (100)LaNiO₃/(111)Pt/TiO₂/(100)Si substrate were both approximately 250, while those on the (100)SrRuO₃//(100)SrTiO ₃ substrate were approximately 220. The temperature dependence of the capacitances for the CaBi₄Ti₄O₁₅ and SrBi ₄Ti₄O₁₅ films on the (100)LaNiO ₃/(111)Pt/TiO₂/(100)Si substrate were approximately+17 and +10%, respectively, in the temperature range from 25 to 400 °C. These values were slightly larger than those of epitaxial BLSD films, but smaller than those of (Ba,Sr)TiO₃ films.