Niobium based Josephson circuit technology

Shuichi Tahara, Hideaki Numata, Shinichi Yorozu +2 more

S. Hasuo

H.‐G. Meyer, G. Wende, Ludwig Fritzsch +2 more

A resonant type of cryoelectronic microwave circuit for the generation of frequency-scaled Josephson voltages is presented. The circuits consist of superconducting microstripline resonators with series arrays of Josephson tunnel junctions located on the microwave current antinodes. This microwave design was chosen to obtain highly accurate Josephson voltages at low microwave power levels and low drive frequencies. The resonator circuits have been fabricated in both niobium-lead and all-niobium technology. At present, we have observed long-term stable Josephson voltages up to 0.75 V for niobium-lead circuits with 1320 junctions and 0.66 V for all-niobium circuits with 1456 junctions, respectively.

E. Mutsenik, S. Linzen, Evgeni V. Il’ichev +7 more

The high kinetic inductance of niobium nitride (NbN) thin films can be used for an implementation of compact on-chip inductances in cryoelectronic circuits. Here, for the first time, we demonstrate the implementation of a hybrid superconducting technology that includes the fabrication of standard aluminum submicron Josephson junctions and the NbN atomic layer deposition process. As an example, we fabricated and characterized a single and array of Al Josephson junctions together with NbN interconnections. The main Al Josephson junction parameters as well as NbN superconducting properties are in a good agreement with the values obtained by our standard fabrication process. The combination of technological processes for the NbN layers with Al Josephson junction allows implementing a new generation of innovative superconducting devices for different applications.

S.L. Thomasson, James M. Murduck, Huang-Tian Chan

Niobium carbonitride (NbCN) Josephson circuits can operate over a wider temperature range than either niobium or niobium nitride circuits. Higher operating temperature places NbCN technology more comfortably within the range of closed-cycle refrigerators, a key factor in aerospace applications. Tunnel junctions have been fabricated from NbCN films with transition temperatures up to 18 K. High-quality NbCN tunnel junction fabrication generally requires low stress films with roughness less than the barrier thickness ( approximately=20 AA). Scanning tunneling microscopy was developed as a tool for measuring and optimizing film smoothness. Junctions formed in situ with AlN tunneling barriers show reproducible I-V characteristics. Unlike NbN, NbCN oxidizes readily, enabling junction definition by a modified SNAP process. This SNAP lithography technique successfully produced NbCn/AlN/NbCN junctions with V/sub m/ values (at 3 mV) up to 27 mV.