Structural and Nanochemical Properties of AlOx Layers in $Al/AlO_x/Al$-Layer Systems for Josephson Junctions

TL;DR

This study investigates how fabrication parameters influence the structural and nanochemical properties of AlOx layers used as tunnel barriers in Josephson junctions, using advanced microscopy and spectroscopy techniques.

Contribution

It provides a systematic analysis of the relationship between fabrication conditions and AlOx layer properties, filling a gap in existing research.

Findings

Oxygen content varies with oxidation parameters.

Amorphous AlOx layers are oxygen-deficient.

Crystalline Al2O3 layers are thicker and stoichiometric.

Abstract

The structural and nanochemical properties of thin $AlO_x$ layers are decisive for the performance of advanced electronic devices. For example, they are frequently used as tunnel barriers in Josephson junction-based superconducting devices. However, systematic studies of the influence of oxidation parameters on structural and nanochemical properties are rare up to now, as most studies focus on the electrical properties of $AlO_x$ layers. This study aims to close this gap by applying transmission electron microscopy in combination with electron energy loss spectroscopy to analyze the structural and nanochemical properties of differently fabricated $AlO_x$ layers and correlate them with fabrication parameters. With respect to the application of $AlO_x$ as tunnel barrier in superconducting Josephson junctions, $Al/AlO_x/Al$-layer systems were deposited on Si substrates. We will show that the oxygen content and structure of amorphous $AlO_x$ layers is strongly dependent on the fabrication process and oxidation parameters. Dynamic and static oxidation of Al yields oxygen-deficient amorphous $AlO_x$ layers, where the oxygen content ranges from x = 0.5 to x = 1.3 depending on oxygen pressure and substrate temperature. Thicker layers of stoichiometric crystalline $\gamma-Al_2O_3$ layers were grown by electron-beam evaporation of $Al_2O_3$ and reactive sputter deposition.