Nb-based Josephson junction devices for nuclear radiation detection: Design and preliminary experimental results

Abstract

In this work we apply the Electrotechnical Laboratory Josephson junction fabrication technology to realize an integrated device for nuclear radiation detection. We have integrated in a single 5×5 mm2 chip 240 Josephson tunnel junctions (JTJs) having various geometrical configurations and interconnections, in order to investigate both the effects of various detection geometrical configurations and the fabrication process uniformity and reproducibility. The junction quality was extensively tested by measurements of the current-voltage characteristics, down to T=1.2 K, showing an unexpected saturation of the Vm quality factor. Preliminary results concerning the response to α-particle radiation of these samples have been obtained. Pulse height and rise time spectra of both ‘‘island’’ type and series connected JTJs are reported. Signals generated by nuclear radiation have been observed at temperatures up to 2 K, where a reduction of the collected charge occurs because of the enhancement of the recombination rate. A strong effect of the substrate on the detector response has also been observed, providing useful indications for future improvements.