Development of ultra-low noise TESs for far-infrared applications

Abstract

The far-infrared (FIR) foreground level in space is extremely low, necessitating highly sensitive detectors for space-based continuum observations. To achieve photon-noise-limited performance, FIR detectors require a noise equivalent power (NEP) lower than 3×10 -19 W/Hz 1/2 and a per-pixel saturation power (P sat ) ranging from 2 fW to 20 fW, as required by the Far-Infrared Imager Polarimeter (FIP) on the Origins Space Telescope (OST). The transition edge sensor (TES), a low-temperature superconducting detector with ultra-low thermal noise, is a promising candidate for FIR astronomy missions. Here we present TESs that meet the NEP requirements for FIR imaging by independently controlling two key parameters, namely the critical temperature (T c ) of the superconducting film and the thermal conductance (G) of the suspended island. These TESs are based on an aluminum-manganese (AlMn) alloy superconducting film deposited on a silicon nitride (Si 3 N 4 ) island. The Tc of the film is tuned by varying the manganese doping concentration and post-deposition annealing temperature. The island is thermally linked to a silicon support structure by four thin (500 nm) and narrow (15 µm) SiN x legs with lengths of 550 µm and 800 µm, allowing precise control of G and thus the NEP. Dark measurements are performed to evaluate the electrothermal characteristics of the devices. The fabricated TESs exhibit an ultra-low NEP of ∼2×10 -19 W/Hz 1/2 , a T c of 56 mK, and a normal resistance (R n ) of 29 mΩ. Their saturation power also meets the specified observation requirement.