Atomic Layer Deposited Materials as Barrier Layers for Preservation of Nb Superconductivity in Multilayered Thin-Film Structures

We have investigated Al_{2}O_{3} as a thin interface material between Nb and polyimide, deposited using a relatively low temperature thermal atomic layer deposition (ALD) process to preserve the superconducting properties of the Nb layer. 250 nm thick Nb traces, with \sim20 nm thick layers of Al_{2}O_{3} were used for this work. HD-4110 spin-on polyimide by HD MicroSystems with a thickness of \sim20 \mum was used with different curing temperatures of 225 °C and 375 °C. DC electrical characterization of patterned Nb lines were carried out using a pulse-tube based cryostat to determine T_{c} and I_{c} for the samples at different steps in the fabrication process. Details of the fabrication processes, experimental procedures and performance results are included. Results of these experiments provide insight into materials stack-ups and fabrication process options for robust, multi-layer superconducting flexible cables that can be used for signal transmission in future densely-integrated cryogenic electronics systems.