Characterization of a Mo/Au Thermometer for ATHENA

The first dark characterization of a thermometer fabricated with our Mo/Au bilayers to be used as a transition edge sensor is presented. High-quality, stress-free Mo layers, whose thickness is used to tune the critical temperature (T_C) down to 100 mK, are deposited by sputtering at room temperature (RT) on Si₃N₄ bulk and membranes, and protected from degradation with a 15-nm sputtered Au layer. An extra layer of high-quality Au is deposited by ex situ e-beam to ensure low residual resistance. The thermometer is patterned on a membrane using standard photolithographic techniques and wet etching processes, and is contacted through Mo paths, displaying a sharp superconducting transition (α ≈ 600). Results show a good coupling between Mo and Au layers and excellent T_C reproducibility, allowing to accurately correlate d_Mo and T_C. Since d_Au is bigger than ξ_M for all analyzed samples, bilayer residual resistance can be modified without affecting T_C . Finally, first current to voltage measurements at different temperatures are measured and analyzed, obtaining the corresponding characterization parameters.