High T/sub c/ SNS step-edge junctions and SQUIDs by using; YBa/sub 2/Cu/sub 3/O/sub 7//CaRuO/sub 3/ double layer

Superconductor-normal-superconductor (SNS) step-edge junction dc SQUIDs were fabricated from YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) films with CaRuO/sub 3/ (CRO) on top as the normal metal. The films were made by pulsed laser deposition (PLD) and patterned by photolithography and ion milling. The junctions and SQUIDs had to be annealed in oxygen environment for a much longer period of time (5-48 hours) compared with standard YBCO film preparation (as deposited or 1 hour), indicating that the top CRO film blocks oxygen in and out of the YBCO film. Before annealing T/sub c/´s of CRO/YBCO double layers and junctions made from them were <70 X and <50 K, respectively, and increased to >88 K and >77 K, respectively after long time annealing. Current-voltage curves of the junctions showed well-behaved resistively-shunted-junction (RSJ) properties and the temperature dependence of the junction critical current was roughly linear. SQUIDs made of those junctions showed voltage modulation in response to applied fields at 77 K.<>