FABRICATION OF HIGH-QUALITY NB/AL-ALOX-AL/NB JUNCTIONS BY A SIMPLE PROCESS

We have fabricated Nb/Al-AlOx-Al/Nb junctions that have extremely low leakage currents by a simple process using only two mask levels. Reducing the thickness of the Al layer under the AlOx improved the quality. For a 20 mu m(2) junction, the current at 0.5 mV at 0.5 K was 4 or more orders of magnitude lower than that at 4.2 K. For 0.70 mu m(2) junctions, the current at 0.5 mV below 1.5 K was 3 or more orders of magnitude lower than that at 4.2 K. We have also fabricated ultra small junctions of high quality. These high-quality junctions can be fabricated by a simple process, hence they are appropriate for various applications.