Influence of Internal Strains of (110)-One-Axis-Oriented (Ba_0.5Sr_0.5)TiO₃ (BST) Thin Films on Their Dielectric Behaviors

We have been proposed a new orientation controlling method using a (101)PdO//(111)Pd buffer layer to deposit (110)-one-axis-oriented perovskite oxide thin films on various kinds of substrates. The (101)-oriented PdO can be obtained by oxidizing (111)Pd and (110)(Ba_0.5Sr_0.5)TiO₃ (BST) was obtained on it by an RF-magnetron sputtering method. The (110)BST thin films fabricated on various substrates, i.e., SrTiO₃, Si, and CaF₂, showed the difference in their dielectric behaviors, which originated from internal strains of the BST films. This internal strain is compress or tensile, which is caused by the difference of thermal expansion coefficients between BST and substrates during cooling them from deposition temperature (700 °C) to room temperature. The internal strains of the (110)-one-axis-oriented BST films affect the dielectric constants and its tunability. The largest tunability was derived on CaF₂, i.e., compressive side, suggesting the internal strain of the BST films affects its capacitance behavior, which is similar behavior reported in (100)-one-axis-oriented-BST films.