A superconducting X-ray spectrometer with a tantalum absorber and lateral trapping

We report the development of Nb-Ta-Al-Al/sub 2/O/sub 3/-Al superconducting tunnel junction structures for high energy resolution and high efficiency X-ray detection. These devices utilize a Ta X-ray absorber with superconductor "bandgap engineered" quasiparticle trapping to improve charge collection. Experimental results at 0.3 K are presented, showing energy resolution of 102 eV full-width-half-maximum for 6 keV X-rays. Collected charge is in excess of 5/spl times/10/sup 6/ electrons. The absorption efficiency is better than 35%. Devices thermally cycle with no change in characteristics.