Development of Cryogenic X-Ray Detectors Based on Mo/Au Transition Edge Sensors

Abstract

Abstract-We report on the development of Mo/Au based Transition Edge Sensors (TESs) aimed at soft X-ray detection. TESs of different sizes with T c~1 00 mK and very narrow transitions have been fabricated. Dark characterization based on I-V, complex impedance and noise measurements has allowed us to obtain their basic functional parameters at different bath temperatures and operating points. Electrodeposited Bi films, to be used as X-ray absorbers, have been developed and characterized.  Index Terms-Transition Edge Sensors, X-ray spectroscopy, proximity effect, radiation detectors

Exploring the Proximity Effect in Mo/Au Bilayers

“…All of them are extremely sharp, with typical transition widths <5 mK. This sharpness, in large area, unpatterned bilayers [15], reveals their uniformity and the high quality of the Mo/Au interface, and therefore the high foreseeable TES sensitivity [13].…”

“…Mo/Au bilayers were deposited at room temperature by magnetron sputtering and electron beam evaporation on top of Si (100) single crystal substrates covered by a low stress Si3N4 layer, 0.5 or 1 m-thick [8,13]. The Mo layers were deposited by RF magnetron sputtering in a UHV chamber, whereas the Au layer deposition procedure is twofold: first a protective Au layer with a thickness of 15 nm is deposited in-situ by DC magnetron sputtering immediately after Mo deposition.…”

“…The two objectives of this deposition procedure are: to avoid Mo surface contamination by covering it in situ, and to reduce the bilayer electrical resistivity by increasing the gold grain size (e-beam provides larger grain sizes than sputtering, and thus lower Au resistivity). Optimum deposition conditions ensuring high quality, strain free Mo layers have been described elsewhere [6,13].…”

Comparison of Different Mo/Au TES Designs for Radiation Detectors

“…Mo/Au TESs with critical temperature Tc~100 mK were fabricated on low stress Si3N4 membranes with thickness 0.5 and 1 m and sizes between 250 and 1000 m. Mo/Au thicknesses, TES components and deposition techniques were as reported previously [4,5]. Refinement of the photolithography procedures [6] has allowed complete dry etching processing, high reproducibility and transition widths of 1-2 mK, even without banks.…”

“…TESs were characterized through I-V curves, complex impedance and noise measurements under DC bias, using the setup described previously [5]. This complete dark characterization was performed at different bath temperatures Tbath and bias currents (bias points).…”