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 non-equilibrium Green's function formalism. Increasing the oxide density is found to produce an exponential increase in the junction resistance. In highly oxygen-deficient junctions we observe metallic channels which decrease the resistance significantly. Computing the charge and current density within the junction shows how variation in the local potential landscape can create channels which dominate conduction. An atomistic approach provides a better understanding of these transport processes and guides the design of junctions for nanoelectronics applications.
Highlights
Superconducting qubits are one of the most promising architectures for quantum computers and are currently the favored technology for many quantum computing groups around the world [1,2,3,4,5]
Fine control of the critical current is highly desirable for creating addressable qubits when fabricating devices containing tens or hundreds of Josephson junctions
In this work we study the interplay between the internal structure of the oxide and its electrical characteristics using a three-dimensional description of the junction
Summary
Superconducting qubits are one of the most promising architectures for quantum computers and are currently the favored technology for many quantum computing groups around the world [1,2,3,4,5]. More detailed analytic models of the tunneling barrier include corrections for temperature, applied voltage, image forces, and asymmetries [10] Two of these models—the Simmons model [11] and the Brinkman, Dynes, and Rowell model [12]—are often used to estimate parameters such as the barrier height and the oxide thickness by fitting to experimental measurements [13,14,15,16,17,18]. There is a growing body of literature in which the nonequilibrium Green’s function (NEGF) formalism is used to calculate the electronic properties of nanoscale devices This is a numerical method which allows us to calculate properties such as the transmission probability, current, and charge density. Variation in the local structure at the Al/AlOx interfaces is shown to affect the uniformity of current flow through the junction
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