Improvement of dielectric tunability and loss tangent of (Ba,Sr)TiO₃ thin films with K doping

Ba_0.6Sr_0.4TiO₃ thin films doped with K were deposited on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method. The structure, surface morphology, and dielectric and tunable properties of Ba_0.6Sr_0.4TiO₃ thin films have been studied in detail. The K content in Ba_0.6Sr_0.4TiO₃ thin films has a strong influence on the material's properties including surface morphology, dielectric and tunable properties. It is found that the Curie temperature of K-doped Ba_0.6Sr_0.4TiO₃ films shifts to higher values compared with that of undoped Ba_0.6Sr_0.4TiO₃ thin films, which leads to a dielectric enhancement of K-doped Ba_0.6Sr_0.4TiO₃ films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices.