We have developed a reliable process to fabricate highhyphen;quality YBa2Cu3O7minus;x(YBCO) superconductorhyphen;normal metalhyphen;superconductor (SNS) stephyphen;edge junctions and SQUIDs over YBCO ground planes. These multilevel circuits employ thin films of SrTiO3and NdGaO3as the insulating layer between the active device and the ground plane and use Ag as the normal metal in the Josephson junction. The reproducibility and uniformity of the junctions are better than our singlehyphen;level devices grown directly on step edges cut into singlehyphen;crystal substrates. Here the critical current variation among junctions on a single wafer is less than a factor of 2. Junctions grown on thinhyphen;film step edges of SrTiO3have critical currents near 2 mA at 4 K, while those grown on NdGaO3step edges have critical currents near 0.5 mA at 4 K.
展开▼
