Optimization and experimental measurements of high impedance niobium-silicon (NbSi) transition edge sensors (TES) for high spectral and spatial resolution x-ray space-borne telescopes

Space-borne x-ray observations of supernova remnants, galactic clusters, x-ray binaries, and black holes are key elements in determining the structure of the universe. Astronomers require wide field of view with high spatial resolution but also very high spectral resolution to determine the physical conditions (temperatures, element abundances) with great accuracy. Today’s technologies (mostly TESs) obtain very high spectral resolutions to the detriment of power consumption, mostly due to their cold stage SQUID readout electronics. Their high power consumption limits the instrument’s field of view (FoV) by constraining the total number of pixels affordable at the 50 mK focal plane of a satellite cryostat. We use a new alloy technology: the high resistivity NbSi, enabling us to design TES sensors promising high spectral resolution and ultra low power consumption (below 10 pW). Their high impedance allows the use of a transistor readout at a hotter stage of the cryostat. This, in conjunction with the inherent ultra-low power dissipation of the sensors, raises drastically the number of pixels of the detector. In this article, we explore pixel optimization ways based on our electro-thermal model to reach spectral resolution of the order of 1.8 eV. We then use this model to manufacture a new batch of pixels on which we conduct experimental measurements. We measure the transient response, energy linearity and noise spectrum of our pixels with an Iron 55 source as well as an innovative on-chip pulse injection system. A low noise cryogenic amplifier as well as a cryogenic experimental setup have been designed to perform these measurements.