Laboratory link : irfu.cea.fr
Astrophysical research requires the development of very high performance cameras embedded in space observatories. The observation of the universe in the X-ray range (X-ray spectro-imagery) needs detectors made of matrices of micro-calorimeters operating at very low temperature (50 mK). The absorption by the detector of an X-ray photon coming from the observed celestial object causes a micro-rise in the temperature of the detector. The measurement of this temperature rise, which makes possible to determine the energy of the photon, requires ultra-sensitive micro-thermometers, and a cryogenic electronics, with very low noise, capable of reading them.
Two technologies of thermometers have been used so far : high-impedance silicon-doped metal insulator sensors (MIS), and very low impedance transition edge sensors (TES). Each requires a very specific electronics, either based on HEMT transistors for adapting to high impedances, or based on SQUIDs for adapting to very low impedances. The high impedances have the advantage of an extremely reduced heat dissipation on the detection stage, which allows a large number of pixels, while the very low impedance TES, more sensitive than the MIS, make easier to obtain excellent spectral resolutions.
A few years ago, a new type of thermometer has been developed by the CNRS/CSNSM : this is high impedance TES, potentially allowing to combine the advantages of one and the other types of detectors. A first thesis was carried out in our laboratory (2016 - 2019), with the aim of evaluating this new path by implementing it for the first time, and by associating it with an innovative readout electronics architecture that performs an active electro-thermal feedback. This thesis has highlighted the extremely promising nature of the device, by obtaining very interesting first experimental measurements.
The objective of the new thesis, proposed here, is to continue this exploratory work by going one new major stage further : validate from this new technology the feasibility of a matrix of several thousand pixels. For this, the work will focus on two parallel axes : on the one hand carry out a complete work of improvement and optimization, in order to draw from the device its best performances, and on the other hand design and test the integrated electronic system (ASIC) essential for the realization of the future large matrices.
The main difficulty lies in the conditions of implementation of the system : the detector must be placed in a cryo-generator to be cooled to very low temperature (50 mK), and equipped with a cryogenic electronics, to be designed, operating at 4 K. This one will have to ensure not only the multiplexing and the amplification of the signal but also, despite this multiplexing, the maintenance of the active electro-thermal feedback of the detectors, and this while satisfying the extremely severe noise and thermal dissipation constraints required by space cryogenics.