Tunnel Junction X-ray Detectors Research Articles

Modification of Layer Structures of Superconducting Tunnel Junctions to Improve X-ray Energy Resolution

The layer structure of a Nb/Al-based superconducting tunnel junction (STJ) X-ray detector was modified to improve the energy resolution (\(\Delta E\)) of STJ X-ray detectors by suppressing the recombination of excited quasiparticles in the electrodes. A 100-pixel array of 100 \(\times \) 100 \(\upmu \)m STJs with a symmetric layer structure of Nb (300 nm)/Al-AlO\(_{x}\)(70 nm)/Al (70 nm)/Nb (300 nm) was fabricated. Fabrication yields of the 100 pixels were more than 90 %. The average leak current of the STJ array was 8 nA. The mean \(\Delta E\) of the STJ array was 6.7 \(\pm \) 1.0 eV for 400 eV X-rays. This \(\Delta E\) is the best value reported for Nb/Al STJs.

Low-energy response of superconducting tunnel junction X-ray spectrometers

Thin film structures incorporating metallic superconducting layers and tunnel junctions can be configured as low-energy X-ray spectrometers. We present results obtained when low-energy X-rays are absorbed in niobium films coupled to aluminum layers that serve as quasiparticle traps in an Nb/Al/Al/sub 2/O/sub 3//Al/Nb tunnel junction X-ray detector. The linearity of the pulse height as a function of energy Is discussed along with the energy dependence of the observed resolution and its relation to the broadening mechanisms. A resolution of 14 eV at 1 keV has been measured with our detector cooled to 0.3 K. >