Digital circuits using self-shunted Nb/NbxSi1-x/Nb Josephson junctions

Superconducting digital circuits based on Josephson junctions with amorphous niobium-silicon (a-NbSi) barriers have been designed, fabricated, and tested. Single-flux-quantum (SFQ) shift registers operated with +/- 30% bias margins, confirming junction reproducibility and uniformity. Static digital dividers operated up to 165 GHz for a single value of bias current, which was only marginally slower than circuits fabricated with externally shunted AlOx-barrier junctions having a comparable critical current density of 4.5 kA/cm(2). In comparison, self-shunted a-NbSi junctions enabled a doubling in circuit density. This and their relatively thick 10 nm barriers could increase the yield of complex SFQ circuits. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432065]