HIGH-T(C) MULTILAYER STEP-EDGE JOSEPHSON-JUNCTIONS AND SQUIDS

We have developed a reliable process to fabricate high-quality YBa2Cu3 O7-x (YBCO) superconductor-normal metal-superconductor (SNS) step-edge junctions and SQUIDs over YBCO ground planes. These multilevel circui ts employ thin films of SrTiO3 and NdGaO3 as the insulating layer betw een the active device and the ground plane and use Ag as the normal me tal in the Josephson junction. The reproducibility and uniformity of t he junctions are better than our single-level devices grown directly o n step edges cut into single-crystal substrates. Here the critical cur rent variation among junctions on a single wafer is less than a factor of 2. Junctions grown on thin-film step edges of SrTiO3 have critical currents near 2 mA at 4 K, while those grown on NdGaO3 step edges hav e critical currents near 0.5 mA at 4 K.