Correlating the nanostructure of Al-oxide with deposition conditions and dielectric contributions of two-level systems in perspective of superconducting quantum circuits

TL;DR

This study investigates how fabrication conditions influence the nanostructure and dielectric properties of Al/Al-oxide/Al systems, aiming to reduce noise caused by two-level tunneling systems in superconducting quantum devices.

Contribution

It provides a detailed correlation between fabrication parameters, nanostructure, and two-level system behavior, offering pathways to improve device performance.

Findings

Fabrication conditions significantly affect nanostructure and dielectric properties.

Ultraviolet illumination during oxide formation alters tunneling system characteristics.

Structural understanding guides improved fabrication routes.

Abstract

This work is concerned with Al/Al-oxide(AlO$_{x}$)/Al-layer systems which are important for Josephson-junction-based superconducting devices such as quantum bits. The device performance is limited by noise, which has been to a large degree assigned to the presence and properties of two-level tunneling systems in the amorphous AlO$_{x}$ tunnel barrier. The study is focused on the correlation of the fabrication conditions, nanostructural and nanochemical properties and the occurrence of two-level tunneling systems with particular emphasis on the AlO$_{x}$-layer. Electron-beam evaporation with two different processes and sputter deposition were used for structure fabrication, and the effect of illumination by ultraviolet light during Al-oxide formation is elucidated. Characterization was performed by analytical transmission electron microscopy and low-temperature dielectric measurements. We show that the fabrication conditions have a strong impact on the nanostructural and nanochemical properties of the layer systems and the properties of two-level tunneling systems. Based on the understanding of the observed structural characteristics, routes are derived towards the fabrication of Al/AlO$_{x}$/Al-layers systems with improved properties.