Hans Kraus

Abstract:

We have designed and tested 5 x 5 mm(2) chips containing island type STJs with different geometries, fabricated on Si substrates in the configuration Nb/Al-AlOx/Nb and using a NbN overlayer acting both as wiring and radiation absorber. The aim is to investigate the advantages of the trapping effect due to the Nb layer trap. In fact, for the NbN/Nb bilayer the scattering time is much faster than the values calculated for other Nb based bilayers, leading to more efficient trapping processes. The junctions have been characterized by tunneling and Josephson current measurements down to 0.5 K. Experimental results concerning the response of the devices under X-ray irradiation down to 60 mK are presented and discussed.

Abstract:

Cryogenic detectors with superconducting tunnel junctions can provide an energy resolution improved by at least one order of magnitude compared with standard semiconductor detectors. While the detection principle was already demonstrated many years ago, the past years were dedicated to the transition from the laboratory sample to practical detectors. Our most favored detector design gives rise to tunnel junctions with electrodes of unequal energy gaps. In such hetero tunnel junctions bias conditions can be established which cause a negative signal current. We report the experimental verification of this effect, and we discuss the yield of charge signal of cryogenic detectors based upon superconducting tunnel junctions. © 1996 Plenum Publishing Corporation.