Effect of strain on tunability in Ba0.60Sr0.40TiO3 thin films on Pt–Si substrates.

Ba0.6Sr0.4TiO3 films with a thickness of 200 nm were deposited on Pt–Si substrates at 400 and 700 °C. Room-temperature tunability was measured and found to improve with deposition temperature, but losses also increased. The dielectric constant, tunability, and loss tangent are found to be 350, 52%, and 0.07 at 300 kV/cm for the 700 °C deposition. The film grown at 700 °C has a larger grain size, leading to approximately 5% higher tunability compared to the film deposited at 400 °C. Supporting theoretical calculations were carried out using a modified Landau-Devonshire thermodynamic formalism that takes into account the internal stresses that arise from the differences of coefficients of thermal expansion between the film and the substrate. [ABSTRACT FROM AUTHOR]