The role of titanium in electromigrated tunnel junctions

TL;DR

This paper investigates how titanium adhesion layers influence the stability and electrical properties of electromigrated gold tunnel junctions, revealing titanium's native oxide as a key barrier component.

Contribution

It demonstrates the crucial role of titanium in enhancing junction stability and identifies titanium native oxide as the tunnel barrier in gold-titanium devices.

Findings

Gold on titanium junctions are more stable at ambient conditions.

Pure titanium junctions exhibit exceptional electrical stability.

The titanium native oxide forms the tunnel barrier in gold-titanium junctions.

Abstract

A standard route for fabrication of nanoscopic tunnel junctions is via electromigration of lithographically prepared gold nanowires. In the lithography process, a thin adhesion layer, typically titanium, is used to promote the adhesion of the gold nanowires to the substrate. Here, we demonstrate that such an adhesion layer plays a vital role in the electrical transport behavior of electromigrated tunnel junctions. We show that junctions fabricated from gold deposited on top of a titanium adhesion layer are electrically stable at ambient conditions, in contrast to gold junctions without a titanium adhesion layer. We furthermore find that electromigrated junctions fabricated from pure titanium are electrically exceptionally stable. Based on our transport data, we provide evidence that the barrier in gold-on-titanium tunnel devices is formed by the native oxide of titanium.