Superconducting tunnel junction (STJ) X-ray detector is promising for materials analysis because of its high energy resolution and high counting rate capability . In order to achieve high sensitivity comparable to a silicon drift detector which has typical sensitive area of 10-100 mm2, it is necessary to enlarge the size of an STJ pixel. We have fabricated 100-pixel STJ array with pixel size of 200 μm having layer structure of Nb-Al/AlOx/Al-Nb. Current – voltage (I-V) characteristics of 100-pixel STJ were measured more than 10 times at 0.3 K. Between each measurement, the temperature was raised more than Tc of Nb. Subgap current values at 0.3 mV were less than 10 nA in 90 pixels out of 100 pixels. The sensitivity of the 100-pixel STJ array is four times higher than in previous studies . When comparing a series of IV curves focusing on a single pixel, the curves show several typical excesses. The fact suggests that the excess current is due to trapping of fluxoids. Possible sources of trapped magnetic fields are Ni plating of wiring materials and leakage of ambient magnetic fields through a magnetic shield. By reducing the residual magnetic field, larger sized STJs can be used.
 Shiki, S., Ukibe, M., Kitajima, Y. et al. X-ray Detection Performance of 100-pixel Superconducting Tunnel Junction Array Detector in the Soft X-ray Region. J Low Temp Phys 167, 748–753 (2012). https://doi.org/10.1007/s10909-012-0526-6
Keywords: Josephson junction, X-ray spectroscopy, Current-voltage characteristics