Small Size Transition-Edge Sensors for Future X-Ray Applications

Large arrays of transition edge sensors (TESs) are the baseline for a number of future space observatories. For instance, the X-ray integral field unit (X-IFU) instrument on board the ATHENA space telescope will consist of ∼ 3000 TESs with high energy resolution ( 2 eV at X-ray energies up to 7 keV). In this contribution we report on the development of an X-ray TES array as a backup detector technology for X-IFU. The baseline readout technology for this mission is time domain multiplexing where the detectors are DC biased. Specifically, we report on the characterization of four different Ti/Au TESs with the following dimensions ( L×W ): 30× 15 , 30× 30 , 50× 25 and 50× 50 μm^2 , all of which are coupled to a 2.3 μm thick Au absorber of area 240× 240 μm^2 . We have performed our characterization using our standard frequency domain multiplexing readout connecting only pixels at low frequencies, where nonlinear effects due to the AC biasing are negligible. Promising energy resolution has been obtained, for instance 1.78± 0.10 eV and 1.75± 0.10 eV at 5.9 keV for the 50× 25 and 50× 50 μm^2 detectors respectively. Uniformity over a kilo-pixel array (of detectors with the same geometry) has been also studied, confirming the high quality of our fabrication process.