Fabrication of nanobridge Josephson devices using Nb thin films (11.1)

Xixi Liu, Xiaoyu Liu, Hao Wang +2 more

Nobumitsu Hirose, Y. Harada, Matsuo Sekine +2 more

Takashi Tachiki, Kenji Horiguchi, Takashi Uchida

To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF 4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 – 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.

Paola Barbara, G. Costabile

Yoshinori Uzawa, Etsuo Kawate, Nobumitsu Hirose +5 more

All-niobium thin-film nanobridges were fabricated with bridge sizes of 40-nm length, 50-nm width, and 100-nm thickness. We investigated the performance of the nanobridges by monitoring Shapiro steps induced on the current-voltage curves by an optically pumped far-infrared laser. These steps have been observed up to 693 GHz (433 μm). This is a twofold increase over that previously reported on thin-film nanobridges.

Tom Godfrey, John C. Gallop, David Cox +3 more

Superconducting QUantum Interference Devices (SQUIDs) based on nanobridge junctions have shown increasing promise for single particle detection. This paper describes the development of the fabrication of improved and reproducible nanobridge junctions fabricated by focused ion beam (FIB) milling from niobium thin films. Although the very low noise properties of nanobridge SQUIDs are well known, the nature of the milling process is little understood at the level of local superconducting properties. In this paper, we report the results for nanobridge Josephson devices and SQUIDs, which we believe are the first to be made by Xenon (Xe) FIB milling. Temperature-dependent current-voltage behavior, microwave-induced Shapiro steps, and SQUID response to magnetic fields have been measured. We make preliminary comparisons with nominally identical devices milled from Nb thin films using either Xe or Ga ions.