STABILITY OF HIGH-QUALITY NB/ALOX/NB JOSEPHSON-JUNCTIONS

We fabricated Nb/AlO(x)/Nb Josephson junctions which showed excellent I-V characteristics (V(m) = 80 mV at the critical-current density of 1500 A/cm2). We attribute these characteristics to the clear junction interface, obtained by depositing Nb and Al layers with a minimum of thermal and physical damage. We fabricated 10(4) junctions connected in series on a single chip with an area of 5 x 5 mm2. Each junction is 10 x 10-mu-2. These junctions have excellent uniform critical currents, have not failed, and have not changed after room-temperature storage for 4 years. These results indicate that Nb/AlO(x)/Nb junctions are excellent for use in Josephson LSI circuits. However, it may be further necessary to improve the uniformity of Al and Al-oxide layers if they are used in an actual large-scale integrated circuit, where more than 10(5) junctions are contained. The influence of the flux trap on current uniformity and deterioration of the I-V characteristics by annealing may be critical for large-scale integration.