The measurements of dc Josephson and quasiparticle current-voltage characteristics of four-layered Nb/Al–AlOx–Nb devices with a fixed Nb thickness of 270 nm and Al thicknesses ranging from 40 to 120 nm are reported and analyzed in the framework of a microscopic model developed to determine stationary properties of dirty limit double-barrier junctions. It is shown that the temperature dependence of the supercurrent as well as the values of characteristic voltages are well reproduced by the model calculations with only one fitting parameter. We have revealed a hysteretic-to-nonhysteretic transition in the current-voltage characteristics of our junctions at temperatures near 4.2 K and argue that this effect is caused by two factors: high-transparency insulating barrier with a broad distribution of the transmission coefficient and the temperature as a tuning parameter, which decreases the McCumber–Stewart parameter from values above unity at low temperatures to less than one above 4.2 K. Finally, we show how and why the temperature stability of the proposed Josephson devices can be significantly improved by choosing an appropriate Al thickness.

We report low-temperature measurements of current-voltage characteristics for highly conductive Nb/Al-AlO x -Nb junctions with thicknesses of the Al interlayer ranging from 40 to 150 nm and ultrathin barriers formed by diffusive oxidation of the Al surface. In a superconducting state these devices have revealed a strong subgap current leakage. Analyzing Cooper-pair and quasiparticle currents across the devices, we conclude that the strong suppression of the subgap resistance compared with conventional tunnel junctions is not related to technologically derived pinholes in the barrier but rather has more fundamental grounds. We argue that it originates from a universal bimodal distribution of transparencies across the aluminum oxide barrier proposed earlier by Schep and Bauer (1997 Phys. Rev. Lett. 78 3015). We suggest a simple physical explanation of its source in the nanometer-thick oxide films relating it to strong local barrier-height fluctuations in the nearest to conducting electrode layers of the insulator which are generated by oxygen vacancies in thin aluminum oxide tunnel barriers formed by thermal oxidation.

We present an ultra high sensitive three-dimensional nano Superconducting QUantum Interference Device (nanoSQUID) fabricated by using the Focused Ion Beam sculpting technique. Based on a fully niobium technology, the nanodevice consists in a niobium superconducting loop (0.2 μm2) interrupted by two nanometric Nb/Al-AlOx/Nb Josephson junctions. The nanoSQUID exhibited an intrinsic magnetic flux noise as low as 0.65 μΦ0/Hz1/2 corresponding to a spin noise less than 10 Bohr magnetons per unit of bandwidth. It has been successfully employed in nanoparticle magnetic relaxation measurements. Due to its excellent performance, reliability, and robustness, we believe that the proposed nanoSQUID offers a crucial step toward a wide employment of nanoSQUIDs in the nanoscience

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