Fabrication and characterization of electrically tunable high-Tc superconducting resonators incorporating barium strontium titanate as a tuning material

We have made the electrically tunable microstrip resonators by using both high-Tc superconducting and dielectric films. The two-pole resonators employ a dielectric barium strontium titanate film on their centre in the form of flip chip. The superconducting YBa2Cu3Oy (YBCO) and dielectric Ba0.1Sr0.9TiO3 were deposited on the CeO2-buffered sapphire substrate and LaAlO3 substrate, respectively, by a pulsed laser deposition technique. Variations of the relative permittivity, εr, and dielectric loss tangent, tan δ, of the Ba0.1Sr0.9TiO3 were studied as a function of the applied dc bias at liquid-nitrogen temperature. The tunability, defined as C(0V)/C(100 V), and loss tangent of the resonators were measured to be ∼1.9 and 1.5x10-2 (at 100 V), respectively. (author)