Investigation of Superconducting Ti/Ti-Au/Au Tri-Layer Films With a Co-Sputtering Process for Transition-Edge Sensors

Abstract

The critical temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> c) of superconducting Ti/Au bilayer films is crucial for the performance of transition-edge sensors. We use a co-sputtering technique to insert a Ti-Au mixture layer as an artificial diffusion layer between a supercon-ducting Ti film and a normal Au bilayer. The Ti-Au mixture layers have different thicknesses and component ratios. The cross-section and element information of thin films was characterized by a high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The variation of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> c is meas-ured for a series of Ti/Ti-Au/Au films. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> c is related to both the thickness and Ti-Au ratio in the mixture layer. We attempt to model the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> c variation based on the Usadel theory with an equiva-lent thickness ratio.