Diffusion Behaviour in Superconducting Ti/Au Bilayers for Transition Edge Sensors to be Applied in Satellite Detectors

Abstract

Controlling the superconducting critical temperature (TC)of Ti/Au bilayers is vital in the development of 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, nor is there a clear explanation for the observed degradation in TC. Here we attempt to explain the change in TC with a diffusion mechanism. The change in TC has been measured for a set of Ti/Au bilayer samples that have been given a variety of heat treatments, where we found a trend that can be partly explained by an inter-diffusion mechanism. With a theoretical model based on diffusion a safe zone can be defined as a region of bake-out treatments, where the TC is unchanged or not affected beyond the requirements of a practical TES detector. This will shine light on the bake-out and storage condition boundaries of these detectors.