Design and Development of a 224-pixel TES X-Ray Microcalorimeter System for Microanalysis with STEM

Studies of astromaterials provide valuable insights into the formation and evolution of the solar system. To analyze such astromaterials on a sub-micrometer scale, one of the most useful tools is energy-dispersive X-ray spectroscopy (EDS) in conjunction with scanning transmission electron microscope (STEM). The conventional semiconductor-based EDS system is sometimes insufficient to resolve emission lines at closely adjacent energies. A transition edge sensor (TES) X-ray microcalorimeter is a promising solution to overcome this problem. We developed a 64-pixel TES X-ray microcalorimeter array which had an energy resolution of approximately 7 eV (FWHM) at an energy band from B Kα to Cu Kα. However, the counting rate was only approximately 1000 count/s/array. The distance between the detector and the sample is 30 cm, limited by the stage of the refrigerator. Therefore, an X-ray polycapillary is used to focus the X-ray, which focus size is 5 mm in diameter, resulting in a detection efficiency of only 5%. To increase the effective area, we developed a large size absorber with a large-scale array. A three-dimensional structure was created to fill the dead space between TES pixels. Additionally, an array of 224 elements was made to increase the detection efficiency by a factor of 10. In this paper, we provide more details of design, fabrication process of the overhang absorber, and device performance.