Stacked Nb-MoSi₂-Nb Josephson junctions for AC voltage standards

Superconductor-normal metal-superconductor (SNS) Josephson junctions have proven to be a critical technology for voltage standards. NIST has used SNS junctions for both dc and ac programmable voltage standards. Previous devices have used primarily PdAu as a normal-metal barrier material. In this paper we present measurements of circuits having MoSi₂ barriers. Stacking enables the junctions to be packed more densely, thus increasing design flexibility and margins for the microwave circuits. In this work, measurements are presented from two-and three-junction stacks for application to ac Josephson voltage standards, which show output voltage and distortion near our best previously published results.