Observation of fluctuation-induced tunneling conduction in micrometer-sized tunnel junctions

TL;DR

This study reports the observation of fluctuation-induced tunneling conduction in micrometer-sized Al/AlO$_{x}$/Y tunnel junctions, highlighting a distinct charge transport mechanism linked to nanoconstrictions and interfacial roughness.

Contribution

First experimental demonstration of fluctuation-induced tunneling conduction in micrometer-sized tunnel junctions with detailed analysis.

Findings

High-$G$ junctions exhibit fluctuation-induced tunneling conduction.

The FITC mechanism is linked to nanoconstrictions and interfacial roughness.

Direct tunneling dominates in low-$G$ junctions.

Abstract

Micrometer-sized Al/AlO$_{x}$/Y tunnel junctions were fabricated by the electron-beam lithography technique. The thin ($\approx$ 1.5--2 nm thickness) insulating AlO$_{x}$ layer was grown on top of the Al base electrode by O$_{2}$ glow discharge. The zero-bias conductances $G(T)$ and the current-voltage characteristics of the junctions were measured in a wide temperature range 1.5--300 K\@. In addition to the direct tunneling conduction mechanism observed in low-$G$ junctions, high-$G$ junctions reveal a distinct charge transport process which manifests the thermally fluctuation-induced tunneling conduction (FITC) through short nanoconstrictions. We ascribe the experimental realization of the FITC mechanism to originating from the formations of "hot spots" (incomplete pinholes) in the AlO$_{x}$ layer owing to large junction-barrier interfacial roughness.