Deposition temperature effect on dielectric properties of (Ba,Sr)TiO3 thin films for microwave tunable devices

(Ba,Sr)TiO3 (BST) thin films were prepared on Pt/Ti/SiO2/Si substrates by RF magnetron sputtering method using a multi-component oxide target at various temperatures, room temperature to 650square. As-deposited thin films were annealed at 650square for 30 minutes under oxygen. Field-dependent dielectric properties were investigated as a function of the deposition temperature. C-V tunability and dielectric loss of the BST thin film were greatly dependent on the substrate temperature during deposition even after the films were post-annealed at 650square. Dielectric constant, tunability and dielectric loss increased with increasing deposition temperature. More stoichiometric (Ba+Sr)/Ti ratio is a major factor for large dielectric constant and tunability in the BST thin film deposited at high temperature. Dielectric loss increased greatly at the deposition temperature above 600square because of rough interface between the BST thin film and bottom electrode. Top-electrode annealing at 600square reduced dielectric loss significantly. The BST thin film deposited at 600square showed the best field-dependent dielectric properties, tunability of 57%, dielectric constant of 368 and dielectric loss of 0.026 at 10 kHz.