Niobium Based Nanoconstrictions With a Josephson-like Electrical Behavior

Superconducting nanoconstrictions have been fabricated from narrow microstrips of Nb deposited by ultra- high vacuum DC sputtering. The thickness of the nanoconstriction has been defined with two different techniques, Ga+ Focused Ion Beam sculpting and Ar+ sputter etching, producing devices that behave as Josephson junctions. A detailed morphological and electrical characterization of the nanoconstrictions has been performed to compare the results obtained with the two techniques. The effect of the electrochemical anodization process used to passivate the film surface and the temperature dependence of critical currents of the devices have also been measured. Different device configurations, single junctions, small series arrays and nanoSQUIDs, have been fabricated, to evaluate the reproducibility and uniformity of the two fabrication processes.