Towards Mo/Au based TES detectors for Athena/X-IFU

摘要

The X-ray spectroscopy telescope Athena has been designed to implement the science theme "the hot and energetic universe", selected by the European Space Agency as the second large mission of its Cosmic Vision program. X-IFU, one of the two interchangeable focal plane instruments of Athena, is a high resolution X-ray spectrometer made of a large array of Transition Edge Sensors. Two options are under consideration for the X-IFU microcalorimeters: Ti/Au bilayers or Mo/Au bilayers. Here we report on our efforts to develop Mo/Au-based TES. The TES are made of high quality superconducting Mo/Au bilayers fabricated at room temperature on low stress Si_3N_4 membranes; Mo is deposited by RF magnetron sputtering and in-situ covered by a thin (15nm) Au layer deposited by DC sputtering; in a second step, the Au layer thickness is increased ex-situ by e-beam deposition, to obtain suitable resistance R_n and operation temperature values. Very sharp transitions (～few mK transition width) are obtained, with typically R_n～25mΩ and T_c～ 100-120mK for 65/215 bilayers. First simple TES designs are being tested. Also, Bi films several urn thick, intended to constitute the X-ray absorber, are fabricated by electrochemical deposition.