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R.L. Kelley, K.R. Boyce (NASA/Goddard Space Flight Center), M. Galeazzi (Department of Physics, University of Wisconsin), K.C. Gendreau (NASA/Goddard Space Flight Center), W. Liao, D. Liu, D. McCammon (Department of Physics, University of Wisconsin), S.H. Moseley, F.S. Porter, C.K. Stahle, A.E. Szymkowiak (NASA/Goddard Space Flight Center), P. Tan (Department of Physics, University of Wisconsin)
We have been developing x-ray microcalorimeters for high resolution x-ray spectroscopy with high quantum efficiency. Detector systems have been developed for sounding rocket experiments to measure the soft diffuse x-ray background (XQC) and as an instrument (XRS) for the Astro-E observatory. The thermometers in these devices are based on ion-implanted silicon to form a sensitive thermistor, and HgTe is typically used to absorb and thermalize x-ray photons. The optimization of these devices depends on the required quantum efficiency and pixel area. Ion-implanted silicon is well suited for the fabrication of arrays, but excess noise in the thermistor has limited the energy resolution. Devices for the soft x-ray background have a resolution ranging from 5 eV to ~ 12 eV over the 0.05 - 1 keV band while devices for the XRS have a resolution of about 9 eV below ~ 1 keV and about 12 eV at 6 keV. Efforts are now underway to reduce this (1/f) noise component by using a technique to increase the thickness of the thermometer, thereby reducing 2D effects in the electron transport. If successful, this approach should significantly improve the performance of implanted-Si microcalorimeters and could be available for near-term use (e.g., sounding rocket payloads, explorer missions, Astro-E2). We will discuss progress on implanted-Si microcalorimeter arrays, and discuss other enhancements for fully realizing the potential of these devices for high resolution, high efficiency x-ray spectroscopy.
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