Structural and dielectric characterization of SrTio3 and BST thin films for microwave applications

Heteroepitaxial SrTiO₃ and polycrystalline Ba_(1-x) Sr_xTiO₃ (x = 0.35, 0.40, 0.50) thin films (~300 nm) were deposited on (100) oriented LaAlO₃ single crystal substrates by pulsed laser deposition using a KrF excimer laser (λ = 248 nm). RBS, XRD, FESEK and AFM were used for structural characterization. The stoichiometry was found to be closest to ideal at higher temperatures around 750°C. The SrTiO₃ films were confirmed to be epitaxial with XRD omega scans, while the BST films were polycrystalline. The permittivity and loss tangent of the films were measured in the range of 1 kHz to 1 MHz. Both materials showed a high dielectric constant 230 for ST and around 800 for BST at room temperature, with losses on the order of a few percent. The tunability of BST was also measured and found to be up to 35%, depending on composition. In addition, correlations between film morphology, processing conditions, and stoichiometry are discussed