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

Abstract

We fabricated YBa₂Cu₃O_7−x/PrBa₂Cu_2.8Co_0.2O_7−y/YBa₂Cu₃O_7−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-μm-wide, 3- to 12-μm-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.