Biepitaxial Josephson junctions with high critical current density based on YBa2Cu3O7−δ films on silicon on sapphire

High-current-density Josephson junctions have been produced in high-temperature superconducting YBa2Cu3O7−δ films deposited on silicon on sapphire and using biepitaxial grain boundaries. The technique is estimated to be useful in integrating superconducting and semiconducting components. A multilayer system of epitaxially grown films was used to form the junctions. A double buffer layer CeO2/ZrO2(9.5% Y2O3) prevented interactions between YBa2Cu3O7−δ and Si during the high-temperature deposition and promoted formation microcrack-free films with a critical current density of 2×106 A/cm2 at 77 K. A MgO seed layer, with (001)MgO∥(001)CeO2 orientation, was used to induce a 45° crystallographic grain boundary in YBa2Cu3O7−δ at its edge. An additional epitaxial buffer double layer of YBa2Cu3O7−δ and SrTiO3 on top of the seed layer promoted the formation of a grain boundary of better crystallinity and stoichiometry. It improved the critical current of the junction about tenfold and resulted in characteristic IcRn products of 150 μV at 77 K in microbridges crossing the grain boundary. Microwave-induced steps were detected at 77 K up to voltages corresponding to the characteristic IcRn value. Peak-to-peak responses to superconducting quantum interference devices reached values of 7 μV at 77 K.