Effect of atomic structure on the electrical response of aluminum oxide tunnel junctions

Abstract

Many nanoelectronic devices rely on thin dielectric barriers through which electrons tunnel. For instance, aluminium oxide barriers are used as Josephson junctions in superconducting electronics. The reproducibility and drift of circuit parameters in these junctions are affected by the uniformity, morphology, and composition of the oxide barriers. To improve these circuits the effect of the atomic structure on the electrical response of aluminium oxide barriers must be understood. We create three-dimensional atomistic models of aluminium oxide tunnel junctions and simulate their electronic transport properties with the nonequilibrium Green's function formalism. With this approach we are better able to understand the role that fluctuations in the density and stoichiometry of the oxide play in the electrical response of the junctions. For instance, increasing the oxide density produces an exponential increase in the junction resistance. In addition we observe the formation of metallic channels in highly oxygen-deficient junctions. We find that local variations in density or stoichiometry can lead to localized conduction channels, even for a junction of uniform thickness. The atomistic approach we have taken provides a better understanding of these transport processes and guides the design of junctions for nanoelectronics applications.