Nb/Al-AlO_x-Al/Ta/Nb Josephson junctions for x-ray detection

摘要

Nb/Al-AlO_x-Al/Ta/Nb Josephson junctions for use as energy resolving x-ray detectors have been fabricated. The junctions have been designed to raise both creation and collection efficiency of quasiparticles. The current-voltage characteristics of the junctions have been investigated on the Al deposition dependence, and found that the characteristics are strongly dependent on the Al deposition rate during the fabrication. The subgap leakage current of those junctions fabricated at higher Al deposition rates exhibit very low leakage current (less than 200 nA at a bias voltage of 100 μV measured at 0.5 K).