Co-Sputtered Amorphous NbₓSi_1 - x Barriers for Josephson-Junction Circuits

Co-sputtered amorphous Nb x Si 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 x Si 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