Micro-machining of a cryogenic imaging array of transition edge x-ray microcalorimeters

Bruijn, M P, Ridder, M, DE Korte, P A J, Moktadir, Z, Wiegerink, R, Berenschot, E and Elwenspoek, M (2001) Micro-machining of a cryogenic imaging array of transition edge x-ray microcalorimeters. Sensor Technology Conference 2001, Enschede, The, Netherlands. 13 - 14 May 2001. pp. 179-184 .

Abstract

Future X-ray Astronomy missions, such as Constellation-X (USA) and the X-ray Evolving Universe Spectroscopy Mission (XEUS, Europe) require detectors with very challenging specifications. For the high energy spectrometer (0.2 to 10 keV) for XEUS the aims are an energy resolution, DEFWHM< 2 eV at 1 keV and DEFWHM< 5 eV at 7 keV, high absorption efficiency, > 90% up to 7 keV, a counting rate > 4 kHz, and an imaging capability of typically 32x32 pixels. The type of detector which is considered as most promising is an array of voltage biased superconducting transition edge microcalorimeters, operated at sub-Kelvin temperatures. The array will be read out using SQUID amplifiers. Based on a successful development of single pixel microcalorimeters, (SRON recently demonstrated an energy resolution DEFWHM< 4.5 eV at 5.9 keV combined with an effective time constant of 150 μs), a project was started to demonstrate this performance in a small array of 5x5 pixels. From the options for design and read-out of imaging arrays, that were considered the past two years, two options survived until now. Both require a large deal of surface and bulk micro-machining. We will present here possible fabrication routes for creating a metal pixel structure on a small perforated nitride membrane. Key element is the use of a sacrificial layer, which can be removed from front or backside of the wafer. Critical issues in the fabrication process will be identified.

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