Design of ultra-low noise AlMn transition edge sensor for far-infrared applications

Future far-infrared (FIR) astronomy missions will need large detector arrays with high sensitivity. Low noise detectors with a noise equivalent power (NEP) of 3×10⁻¹⁹ to 1×10⁻²⁰ W/Hz1/2 for space-based continuum observations are needed, to be photon noise limited. Transition edge sensor (TES) as a type of sensitive low-temperature superconducting detector, has significant advantages in the measurement of broad band electromagnetic radiation, from millimeter waves to X-ray and gamma-rays. We propose a design of low noise TESs for FIR applications, with the NEP of lower than 3×10⁻¹⁹W/Hz1/2. The key component on TES bolometer island is aluminum-manganese (AlMn) superconducting film, which has been proved that its critical temperature can be adjusted over a wide range by baking after the film deposition. We optimize the NEP of AlMn TESs by reducing the critical temperature to around 60 mK and designing the thermally isolating legs to reduce the thermal conductance effectively. The pixel design will be used as foundation in our future TES array designs and will benefit high-sensitive detector development.