Epitaxial heterostructures of YBa2Cu3O7-delta/KTaO3 and YBa2Cu3O7-delta/BaxSr1-xTiO3 for tunable microwave components

Heterostructures with a thin BaxSr1-xTiO3 or KTaO3 ferroelectric layer between two YBa2Cu3O7-delta superconducting films were laser deposited on a buffered Si-on-sapphire substrate. The top and bottom YBa2Cu3O7-delta films were well c-axis oriented and free from micro-cracks and had superconducting transitions T-c in the range 88-90 K. The dielectric permittivity, epsilon(r), and the high-frequency losses of epitaxially grown BaxSr1-xTiO3 and KTaO3 layers were measured in the temperature interval 15-300 K (f = 100 kHz).