Large Arrays of TES X‐ray Microcalorimeters for Dark Baryon Search

Arrays of transition edge sensor (TES) X‐ray microcalorimeters can provide a high energy resolution and a large area necessary for future dark baryon search missions such as DIOS (Diffuse Intergalactic Oxygen Surveyor). In the current design, the energy resolution of 2 eV at 0.3–1.5 keV and the geometrical area of 1 cm2 are required for DIOS. As an R&D study, we fabricated a 16×16 Ti/Au bilayer TES array without an absorber, and achieved the energy resolution of 4.4±0.2 eV at 5.9 keV. Considering the recent experimental results on so‐called excess noise, we investigated a detailed design of the TES array for DIOS. We concluded that we need a at least 20×20 pixel array consisting of 250 μm‐square TESs and 500 μm‐square mushroom‐type Bi/Au absorbers. We discussed technical issues to manufacture such a large format array.