Co-Sputtered Amorphous Nb $_{ x}$ Si $_{1 - { x}}$ Barriers for Josephson-Junction Circuits

Co-sputtered amorphous Nb_xSi_1-x has been developed as a barrier material for Josephson-junction array circuits. This material is quite promising as a normal-metal barrier for state-of-the-art Josephson voltage standards. In addition, the capability of tuning the barrier resistivity over a wide range that includes the metal-insulator transition could lead to applications in high-speed superconductive electronics. The electrical characteristics and uniformity of amorphous Nb_xSi_1-x-barrier junctions are similar to those of other normal-metal barriers, but the superior etching properties makes this barrier material especially promising for tall, stacked junctions that are required for high-junction-density applications. Under appropriate deposition conditions, the reproducibility of devices with co-sputtered amorphous NbxSi_1-x is sufficient to produce high-quality stacked-junction superconductive devices