Properties of Large-Sized Nb-Based Superconducting TunnelJunctions for X-Ray Detection

Niobium-based superconducting tunnel junctions are expected to be applicable to high-resolution X-ray measurements. Large-sized tunnel junctions with a Nb/Al/AlO x /Nb structure have been fabricated in order to study their performance in X-ray detection. The niobium layer which was sensitive to X-rays had a large size of 100 µm square ×1.2 µm thick. The junction detected 5.9 keV X-rays with an energy resolution of 1 keV. On the basis of the experimental data, the junction parameters were studied to produce a better energy resolution than that of silicon semiconductor detectors. The microstructure of the aluminum layer was observed by means of a transmission electron microscope.