Effect of Interface Structure on Electrical Properties of (Ba,Sr)TiO₃ Thin Films on Glazed Alumina Substrate

Abstract

We examined the impact that the electrode/(Ba,Sr)TiO3 (BST) interface structures have on electric properties by investigating the electrical conduction mechanism of the BST thin-film capacitors with Pt and Au top electrodes. The BST thin films were prepared on the Pt bottom electrode/glazed Al2O3 substrate by chemical solution deposition (CSD). The dielectric property of the as-deposited Pt/BST/Pt capacitor had a large frequency dispersion and the leakage current properties deteriorated because the Pt top electrode/BST interface structure is rough. However, by post-annealing for 30 min at 400 °C after the top electrode was deposited, the frequency and temperature properties improved. The Schottky barrier height at the Pt top electrode/BST interface was 1.03 eV and that at the Au/BST interface was 0.73 eV, which indicated that its electrical conduction mechanism depends on the Schottky emission model. The dielectric constant, tan δ, and tunability of the Au/BST/Pt capacitor are 200, 0.0178, and 53.7% (at 214 kV/cm, 6.0 V), respectively, which showed excellent dielectric properties. This suggests that high-quality BST films for application to tunable microwave devices can be formed on a very inexpensive glazed Al2O3 substrate.