Fabrication of bridge-type microcalorimeter arrays with Ti-Au transition-edge-sensors

The present stage of cryogenic detector development is focused on fabrication of arrays. Arrays of superconducting-transition-edge-sensor (TES) microcalorimeters have generally been fabricated on SiNX membranes. In conventional membrane structures fabricated by backside etching, it is difficult to realize arrays having both mechanical toughness and a large filling factor. It is possible to overcome these difficulties by using a bridge-type membrane structure, in which SiNX membranes are raised above the Si substrate with a gap of 10-50 μm. In order to carry out etching and other processes, we have fabricated a small scale array with a bridge-type membrane structure. A preliminary version of a TES microcalorimeter array with a 5x5 pixel structure had dimensions of 6x10 mm2. Each pixel consisted of a Ti/Au bilayer with a size of 0.5x0.7 mm2 on a 1 μm-thick SiNX membrane of 0.7x2 mm2. Although the current array exhibited a small filling factor of about 0.1, it is possible to obtain a high filling factor by fabricating mushroom-shaped absorbers