Energy resolving X-ray detectors using niobium absorbers and multiple quasiparticle tunneling between two aluminum traps

Superconducting tunnel junction devices are being developed for use as high-resolution, high-efficiency X-ray spectrometers. A device with niobium X-ray absorbing layers coupled to two aluminum layers on either side of the tunneling barrier which serve as quasi-particle traps has been tested. These devices were fabricated photolithographically using a modified niobium/aluminum/niobium trilayer fabrication process. The first devices have a very thin barrier with specific normal state resistance of 1.5*10/sup -6/ Omega -cm/sup 2/, and also exhibit very low leakage current (<15 nA below 200 mK). The energy resolution at 6 keV was 120 eV full width at half maximum. It is estimated that each quasi-particle tunnels an average of eight times before recombining, increasing the total charge transferred and decreasing the effects of electronic noise.<>