Hans Kraus

Abstract:

Cryodetectors with superconducting sensors have been actively developed and optimized during the past years. This review discusses the operating principles of the two detector concepts, superconducting tunnel junctions and low-temperature bolometer or calorimeter. Progress in research with cryodetectors manifested itself by many successful device demonstrations and as a result, a shift in emphasis from pure detector optimization towards actual applications has been observed. Cryodetectors have been used for X-ray fluorescence, optical photon detection, mass spectroscopy of heavy molecules, etc. Nevertheless, there is still room for further improvement until the detectors will have actually reached their theoretical limitations.

Abstract:

Superconducting bolometers and calorimeters are used in many applications, such as infrared astronomy, fast spectroscopy of condensed matter excitations or even in particle physics and plasma diagnostics. The development in this field has a long history and is very active and numerous successful applications can be counted. Many of the detectors discussed in this article make use of the steepness of the resistance-temperature characteristics at the transition between the normal and superconducting phase of superconductors. This overview includes low-TC calorimeters, mainly for applications to particle and astrophysics, and high-TC bolometers which could replace presently used detectors. In addition, related detection techniques will be addressed.

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.