Dependence of Mo/Au Transition-Edge Sensor Properties on Normal Resistance and Critical Temperature

We have investigated the dependence of superconducting tran sition parameters on the bilayer properties in Mo/Au transition edge sensors (TESs). We present measurements of the normalized partial derivatives of TES resistance with respect to temperature (α) and current (β), in several fabricated wafers with differing bilayer properties, but in a single TES design characterized at the same relative point in the transition. The results show α increases and β decreases approximately linearly with TES temperature T and normal state resistance Rn. To study these dependencies further, we measured the temperature dependence of the critical current Ic(T), and found it decreases approxi mately exponentially at high temperature. The slope of Ic(T) on a logarithmic scale correlates with Rn but is independent of the transition temperature. We examine to what extent these f indings can explain the observed T and Rn dependence of α and β. These results have implications for our understanding of the fundamental physics of the transition in these devices, and the reproducibility of TES performance resulting from small changes in bilayer fabrication.