Superconducting Tunnel Junctions with Multilayer Electrodes as Energy-Resolving X-Ray Detectors

Superconducting tunnel junction X-ray spectrometers promise to combine efficiency and broad bandwidth with high-energy resolution--a combination not available in current commercial detectors. Conductus, Inc., in collaboration with Lawrence Livermore National Laboratory, has begun development of STJ X-ray detectors which use a novel multilayer electrode structure. We have already demonstrated Nb/Al-Al2O3-Al/Nb tunnel junction detectors with about 40 eV resolution for 6 keV X-rays; this is the best resolution ever obtained for any type of STJ detector. Because of their simplicity, bandwidth, resolution and count-rate capability, superconducting tunnel junction spectrometers should be ideally suited for X-ray astronomy applications. In phase I of this project we will optimize the electrode structure for energy resolution and operating temperature. In phase II we will develop large area detector arrays with high quantum efficiency and high spatial resolution.