Read-out electronics for NTD germanium X-ray microcalorimeter arrays

Microcalorimeters for broad-band high-resolution X-ray spectroscopy are a very promising detector technology for future astrophysics and laboratory research applications. In principle, these detectors can achieve a spectral resolution as good as 1 eV in the soft X-ray energy range. The best results obtained in laboratory tests are 2-3 eV @ 6 keV and 50-60 eV @ 50 keV on single pixel devices. Some small arrays have been built and tested, while efforts are being done in the implementation of larger size (» 1,000 pixels) arrays. The INAF-OAPA group has set up an Adiabatic Demagnetization Refrigerator (ADR) aimed at developing and testing X-ray microcalorimeters, which have an operating temperature of about 60 mK, and is presently developing a fully planar process to build arrays of microcalorimeters using Neutron Transmutation Doped (NTD) germanium as temperature sensor. Currently the INAF-OAPA group uses a front-end electronics based on low-noise JFETs to read out signals from single pixel devices. The working temperature of such electronics is 120 K. Limiting the thermal load on the cold stage of the refrigerator where the microcalorimeters are located, imposes long wiring and heat sinks, and restricts this approach to devices with a small number of pixels. We propose to develop a readout electronics suitable for multipixel devices, starting from the single pixel experience, and to test it at XACT facility in Palermo.