Diffusion Behaviour in Superconducting Ti/Au bilayers for SAFARI TES Detectors

Controlling the critical temperature ($T_{C}$) of Ti/Au bilayers is vital in the development of practical TES detectors. Previously empirical studies have been done on aging effects in Ti/Au and other superconducting bilayers but no link with theory has been made. Here we attempt to explain the change in $T_{C}$ with a diffusion mechanism. The change in $T_{C}$ has been measured for a set of Ti/Au bilayer samples that have been given a variety of bake-out treatments, where we found a trend that can be partly explained by an inter-diffusion mechanism. With an empirical model based on diffusion a safe zone can be defined as a region of bake-out treatments, where the $T_{C}$ is not affected beyond the requirements. This will shine light on the bake-out and the storage condition boundaries of these detectors.