Current status of Ir-TES x-ray microcalorimeters at the University of Tokyo

We are developing iridium-based transition edge x-ray microcalorimeters. The superconducting iridium film is very promising as the transition edge sensor because of its sharp transition at the low temperature of 130 mK and its chemical stability for long term stable operations. The single iridium TES of 500 μm x 500 μm size showed very complicated signal responses, that well be explained with the phase separation model. This model is also useful to develop a new position sensitive microcalorimeter. We have fabricated a pixelated TES array, and successfully obtained position readout from ten pixels and the energy resolution of 13.1 eV for 3 keV x-rays. For developing more high-energy resolution detectors, we have fabricated iridium/gold bilayer TES microcalorimeters. This type of device showed the energy resolution of 9.4 eV for 5899 eV x-rays. (author)