Structural and dielectric characterization of SrTio/sub 3/ and BST thin films for microwave applications

Heteroepitaxial SrTiO/sub 3/ and polycrystalline Ba/sub (1-x)/Sr/sub x/TiO/sub 3/ (x = 0.35, 0.40, 0.50) thin films (/spl sim/300 nm) were deposited on [100] oriented LaAlO/sub 3/ single crystal substrates by pulsed laser deposition using a KrF excimer laser (/spl lambda/ = 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/spl deg/C. The SrTiO/sub 3/ 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.