Characterization of aluminum oxide tunnel barriers by combining transport measurements and transmission electron microscope imaging

TL;DR

This paper combines transport measurements and electron microscopy to analyze aluminum oxide tunnel barriers, revealing larger conduction areas than predicted and linking thickness variations to tunneling behavior.

Contribution

It introduces a dual approach using electrical measurements and microscopy to characterize tunnel barrier uniformity and conduction properties.

Findings

Effective conduction area is an order of magnitude larger than theoretical predictions.

Variations in barrier thickness explain increased conduction and higher order tunneling.

Microscopy confirms barrier thickness variations as a key factor.

Abstract

We present two approaches for studying the uniformity of a tunnel barrier. The first approach is based on measuring single-electron and two-electron tunneling in a hybrid single-electron transistor. Our measurements indicate that the effective area of a conduction channel is about one order of magnitude larger than predicted by theoretical calculations. With the second method, transmission electron microscopy, we demonstrate that variations in the barrier thickness are a plausible explanation for the larger effective area and an enhancement of higher order tunneling processes.