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

6 pages, 4 figures