Development of Ta-Based Superconducting Tunnel Junction X-Ray Detector Arrays

Abstract

We are developing new Ta-based superconducting tunnel junction (STJ) X-ray detectors for high-resolution soft X-ray spectroscopy at synchrotrons. STJ detectors combine the high-energy resolution of cryogenic detectors with the high count rate capabilities of athermal devices and the high efficiencies of solid state detectors, which increases the sensitivity for material analysis by fluorescence-detected X-ray absorption spectroscopy. Our STJ detectors are fabricated using thick, high-Z Ta absorber films that enhance quantum efficiency and spectral purity, and extend operational range to several keV compared with earlier Nb-based STJs. They offer an energy resolution of ~ 5 to 10 eV FWHM for soft X-rays up to ~1 keV, and count rates of several 1000 counts/s per detector pixel. For increased solid angle coverage, we have fabricated 36- and 112-pixel Ta-based STJ detector arrays with total areas of 1.4 and 4.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The 208 × 208 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> pixels have an energy resolution between 6.8 and 7.6 eV FWHM at 525 eV with a low-energy shoulder, and their responsivity is uniform to within 2% across the array. Here we discuss the performance of the array in the context of synchrotron science.