Soft X-ray Detection Performance of Superconducting Tunnel Junction Arrays with Asymmetric Tunnel Junction Layer Structure

Abstract

Superconducting tunnel junction (STJ) array detectors with an asymmetric tunnel junction layer structure have been fabricated for the soft X-ray region between 100 eV and 1 keV. The asymmetric layer design was effective in solving the problem of double peak response to monochromatic X-rays, which is commonly observed in STJ detectors. The sensitive area was patterned by a lift-off technique that ensured no contamination on the top Nb electrode surface. The performance of a 100-pixel STJ array detector was investigated through fluorescent X-ray analysis of oxides and nitrides for the energy region of the K-lines of oxygen, nitrogen, and boron. The STJ array detector exhibited a high energy resolution of <15 eV, which cannot be achieved by semiconductor detectors, and an energy nonlinearity of <1%. It was demonstrated that the performance is suitable for fluorescence-yield X-ray absorption fine structure (XAFS) spectroscopy for light trace elements.