Materials and fabrication processes for Nb-Si-Nb SNAP devices

Niobium-amourphous silicon-niobium SNAP junction fabrication has demonstrated great technological promise. An aluminum mask gives good resolution to the anodization process and can then be used to pattern an insulating layer self-aligned with the junctions. If the anodization is carried out using a constant-rate voltage ramp and the anodization current is plotted against the anodization voltage, one has an effective analytic tool for studying the niobium and determining an anodization endpoint. We incorporate thin palladium layers in our devices for three purposes. First, the layers provide for resistors while giving superconducting contact through the layer by the proximity effect. Second, the palladium acts as an etch-stop layer so that the top niobium layer can be plasma-etched without damage to the trilayer. A final palladium layer prevents oxidation and makes possible solder contacts to our devices.