YBaCuO/Co-doped PrBaCuO/YBaCuO ramp-edge junctions and their application to flip-flop circuits

We fabricated YBa2Cu3O7-x/PrBa2Cu2.8Co0.2O7-y/YBa2Cu3O7-x ramp-edge Josephson junctions and measured their current-voltage (I-V) characteristics. Critical current (I-c) and conductance (G) were evaluated as a function of the barrier layer thickness, and both of them exhibited a nearly exponential dependence. The decay parameters for I-c and G were estimated to be 1.1 and 1.5 nm, respectively. We also examined superconducting quantum interference devices (SQUIDs) using this type of junction as a preliminary test for realizing oxide superconductive integrated circuits with high-speed operation. DC SQUIDs with direct-coupling control lines and no ground plane were fabricated and their loop inductance was evaluated. The obtained SQUID inductance ranged From 8 to 38 pH for a 4-mu m-wide, 3- to 12-mu m-long hole in a rectangular SQUID loop. In addition, a flip-flop circuit based on such a dc SQUID was fabricated. Both flux trapping and flux detrapping in the SQUID loop hole were confirmed when 1-ms-wide current pulses were injected into the SQUID loop. (C) 1999 Elsevier Science Ltd. All rights reserved.