A 4-by-4 high impedance NbSi TES array for high resolution X-ray spectro-imaging

We conduct an R&D project on high impedance TES detectors aiming to minimise the focal plane power consumption while having high spectral and spatial resolutions. In this article we review the development of 4-by-4 Niobium-Silicon (NbSi) Transition-Edge-Sensor (TES) arrays. The 16 membrane pixels are suspended by thin (5 μ m thick) Silicon bridges that ensure electrical wiring and a weak thermal link to the heat sink. We fabricate these arrays on Silicon On Insulator (SOI) wafers with different pixel-to-substrate bridge lengths, widths, orientations and numbers to experimentally determine the Silicon heat conduction at 100 mK. We also design different NbSi TES meanders to measure the electron-phonon decoupling effect, the various heat capacities (Si, NbSi, absorber) and the slope of the superconducting transitions. These chips will help to better understand and control the physical parameters for future optimised developments. This constitutes, in addition with our 50 mK CMOS multiplexing ASIC and our 4 K HEMT-SiGe amplifier, a scaled-down prefiguration of an X-ray cryogenic detector chain for astrophysics.