Current‐voltage characteristics of all‐NbN nanobridges

All-NbN nanobridges were developed for the thin-film Josephson mixer in an integrated receiver for the detection of electromagnetic radiation. The transport mechanism of dc current and the product of the critical current-normal state resistance were evaluated. As a result, it was found that when the thickness of an NbN film at the bridge section was (5 ∼ 7) ζ, bulk-like non-Josephson currents, which make the mixer design and operation analysis difficult, were superimposed on the critical current. The value of the non-Josephson current was evaluted quantitatively by measuring the magnetic field dependence of the critical current. The non-Josephson current due to the three-dimensional effect of the current flowing through the bridge section was removed by Ar-ion thinning of the NbN film at the bridge section. The IJRN product was evaluated by using the true Josephson current IJ.

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