NbN, Nb Double-Layered Base-Electrode Josephson Junctions

Abstract
A new structure of the base-electrode for Josephson devices have been developed in which niobium (Nb) and niobium nitride (NbN) films were sequentially sputtered to form a double-layered structure. Owing to this structure, it is possible not only to reduce the kinetic inductance of the base-electrode due to the small penetration depth of Nb film, but also to obtain good tunneling characteristics with a small subgap conductance due to the surface stability of NbN film. Single-flux-quantum (SFQ) memory cells with this structure have been fabricated and it has been observed that the kinetic inductance is much decreased comparing with that of the SFQ cell with a base-electrode of NbN single layer.

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