Fabrication of RS flip-flops using Y-Ba-Cu-O ramp-edge junctions and their operation

We fabricated single flux quantum RS flip-flop circuits by using ramp-edge Josephson junctions and tested their performance. The junctions were constructed with two Y₁Ba₂Cu₃ O_7-x (YBCO) electrodes and a barrier layer. As barrier materials we used cobalt-doped YBCO. To insulate between YBCO layers we used Sr₂AlTaO₆ (SAT) thin films. We also fabricated RS flip-flop circuits by using YBCO ground planes to reduce the inductance of YBCO film. The fabricated Josephson junctions showed typical RSJ-like current-voltage (I-V) characteristics above 50 K. We could successfully demonstrate the correct operation of the RS flip-flop circuits at the temperatures near 50 K. We used a computer controlled digital measurement set-up to test the circuits. The RS flip-flop circuit fabricated on a ground plane showed more definite set and reset states on the voltage-flux (V-φ) modulation curves of the read SQUID than those of the circuit made without ground plane. This may be attributed to the shielding effect by a YBCO ground plane