Investigation of the Superconducting Ti/PdAu Bilayer Films for Transition Edge Sensors

High quality superconducting films are crucial for the development of transition edge sensors (TESs) with high energy resolution ability. Controlling the superconducting transition temperature (T-c) and the transition width (Delta T-c) of the films from the superconducting to normal metal state is important for the performance of TESs. We present a new kind of superconducting Ti/PdAu bilayer film. The influence of Ti/PdAu thickness ratio on T-c through the proximity effect is investigated. The T-c can be tuned from 175 mK to 336 mK by setting the PdAu thickness to 60 nm and varying the thickness of Ti from 50 nm to 70 nm. The minimum Delta T-c is similar to 1 mK. The element distribution at the interface between the Ti and PdAu layers has been analyzed by a high-resolution transmission electron microscopy (HRTEM), energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD). Roughness, electrical resistivity, and cryogenic properties are also shown. The superconducting Ti/PdAu bilayer film shows a great promise as a new material for TESs.