Characterization of Ba0.1Sr0.9TiO3/YBa2Cu3O7–δ heterostructures on vicinal LaAlO3 substrates

Ba0.1Sr0.9TiO3/YBa2Cu3O7−δ heterostructure films have been fabricated by pulsed-laser deposition on LaAlO3 substrates. During the fabrication, a c-axis oriented YBa2Cu3O7−δ thin film with atomically smooth surfaces was epitaxially grown in the step-flow mode on a vicinal LaAlO3 substrate. The superconducting transition temperature Tc was above 88K. Then a single-crystalline Ba0.1Sr0.9TiO3 layer was deposited on top of the YBa2Cu3O7−δ layer. A parallel-plate capacitor configuration was used to measure the capacitance–voltage properties of the Ba0.1Sr0.9TiO3 thin films at 300K and 77K, respectively. The dielectric constant and loss tangent measured at 1MHz and 77K are 1200 and 0.0045, respectively. A tunability of 60% has been achieved under ±30V DC bias, confirming their usefulness for frequency-agile microwave devices.