Dependence of Microwave Properties of BaxSr1-xTiO3 Thin Films on Substrate

Ba x Sr1-x TiO3 (x=0.5) (BST) films were deposited on MgO, c-cut sapphire, r-cut sapphire and Si substrates by rf sputtering. A coplanar waveguide line was fabricated as a transmission line for microwave signals. Both the phase shift and loss tangent of the samples were measured using the on-wafer through-reflect-line (TRL) calibration comparison method. An external bias of 200 V was applied to the coplanar waveguide line fabricated on the BST layer. The phase of the line changes according to the dependence of BST permittivity on bias. The phase of the line was found to vary according to the crystalline quality of the films. The films were epitaxially grown on the MgO and c-cut sapphire substrates. The phase shifts of the samples were 58.4°, 4.4°, 1.5° and 0.7° for samples with films grown on Si, MgO, c-cut sapphire and r-cut sapphire, respectively. The dielectric loss tangents were 0.008, 0.016 and 0.026 for the films grown on MgO, r-cut sapphire and c-cut sapphire, respectively.