Dielectric property controls using crystal structure anisotropy in bismuth layer-structured dielectrics

Temperature dependency of the dielectric property of c-axis-orientcd SrBi₄Ti₄O₁₅ films was investigated in a temperature range from 80 to 400 K. c-axis-oriented epitaxial films with the film thickness of 30 and 140 nm were grown on (100)_cSrRuO ₃//(100)SrTiO₃ substrates by metal organic chemical vapor deposition (MOCVD). Increasing lattice distortions along the aand c-axes with decreasing film thickness was ascertained by XRD reciprocal space mapping. However, capacitance change normalized by the capacitance data at 300 K for with temperature was independent of the film thickness; it increased from 80 to 230 K and contrary decreased with increasing the temperature. Especially, the temperature coefficient of capacitance from 230 to 330 K was almost the same. It indicates that dielectric characteristics of these films for the temperature are independent of the film thickness in the actual use. Moreover, the same mesurement for the 120 nm-thick fiber-textured c-axis-oriented SrBi ₄Ti₄O₁₅ film deposited on the (100) _cLaNiO₃/(111)Pt/TiO₂/SiO₂/(100)Si substrate was also investigated. Resultant capacitance change with the temperature was basically the same with that of the epitaxial one, even though the temperature at maximum capacitance value was slightly shifted to lower temperature of 200 K. These data suggest that of capacitance change with the temperature was almost independent of the film thickness and the in-plane orientation.