Fabrication of sandwich-type MgB2/Boron/MgB2 Josephson junctions with rapid annealing method

摘要

Sandwich-type MgB2/Boron/MgB2 Josephson junctions were fabricated using magnetron sputtering system. The rapid-anneal process was adopted to replace traditional way of annealing, trying to solve the problem of interdiffusion and oxidation with multilayer films. The boron film was used as barrier layer to avoid the introduction of impurities and improve reproducibility of the junctions. The bottom MgB2 thin films deposited on c-plane sapphire substrate exhibits a critical temperature T-C of 37.5 K and critical current density J(C) at 5 K of 8.7 x 106 A cm(-2). From the XRD pattern, the bottom MgB2 thin film shows c-axis orientation, whereas the top MgB2 became polycrystalline as Boron barrier layer grown thicker. Therefore, all junction samples show lower T-C than single MgB2 thin film. The junctions exhibit excellent quasiparticle characteristics with ideal dependence on temperature and Boron barrier thickness. Sub-harmonic gap structure was appeared in conductance characteristics, which was attributed to the multiple Andreev reflections (MAR). The result demonstrates great promise of this new fabrication technology for MgB2 Josephson junction fabrication. (C) 2015 Elsevier B.V. All rights reserved.