Characteristics of Nb junctions with additional Al/Alox

We systematically investigated the characteristics of Nb/Al/AlOx/Al/AlOx/Nb junctions having a structure in which Al/AlOx films are placed in a Nb/Al/AlOx/Nb trilayer junction. The junction characteristics reflect superconductivity in the second Al film due to the proximity effect. As a result, the critical current density J(c) and the hysteresis on its current-voltage (I-V) curve strongly depend on the transparencies of the AlOx barriers. The hystereses of the junctions are smaller than those of Nb/Al/ AlOx/Nb junctions at the same J(c). Intrinsically overdamped junctions are also realized. The intrinsically overdamped junctions can considerably reduce an area occupied by a single gate. Furthermore, the spread of critical current I-c for the junctions, which have hystereses, connected in series, is +/-1.2%. This shows that the junctions with additional Al/AlOx have uniform enough characteristics to be used in integrated circuits. (C) 1999 Elsevier Science Ltd. All rights reserved.