A New Fabrication Process of Superconducting Nb Tunnel Junctions with Ultralow Leakage Current for X-Ray Detection

概要

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A new fabrication process is presented to make Nb/Al/AlO_x/Nb superconducting tunnel junctions with ultralow subgap leakage current at low temperatures below 4.2 K for X-ray detection. A Nb anodization process has been adopted to make electric insulatioun at the periphery of an ultrathin AlO_x tunnel barrier through use in combination with the conventional SiO self-aligned insulation process. The temperature dependence of the subgap current of the junctions fabricated by the present process is in good agreement with that predicted by the Bardeen-Cooper Schrieffer (BCS) theory, while junctions made by the conventional process show a weak temperature dependence of the subgap current. In addition, the Vm value of the junction fabricated by the present process was found to be more than 3000 mV at 1.2 K. It has been clarified that the anodization process introduces improvements to make the subgap leakage current extremely small in the temperature range from 4.2 K down to 1.2 K.
社団法人応用物理学会の論文
1993-10-15