Current-induced energy barrier suppression for electromigration from first principles
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AbstractWe present an efficient method for evaluating current-induced forces in nanoscale junctions, which naturally integrates into the nonequilibrium Green's function formalism implemented within density functional theory. This allows us to perform dynamic atomic relaxation in the presence of an electric current while evaluating the current-voltage characteristics. The central idea consists of expressing the system energy density matrix in terms of Green's functions. To validate our implementation, we perform a series of benchmark calculations, both at zero and at finite bias. First we evaluate the current-induced forces acting over an Al nanowire and compare them with previously published results for fixed geometries. Then we perform structural relaxation of the same wires under bias and determine the critical voltage at which they break. We find that although a perfectly straight wire does not break at any of the voltages considered, a zigzag wire is more fragile and snaps at 1.4 V, with the Al atoms moving against the electron flow. The critical current density for the rupture is estimated to be 9.6 × 1010 A/cm2, in good agreement with the experimentally measured value of 5 × 1010 A/cm2. Finally, we demonstrate the capability of our scheme to tackle the electromigration problem by studying the current-induced motion of a single Si atom covalently attached to the sidewall of a (4,4) armchair single-walled carbon nanotube. Our calculations indicate that if Si is attached along the current path, then current-induced forces can induce migration. In contrast, if the bonding site is away from the current path, then the adatom remains stable regardless of the voltage. An analysis based on decomposing the total force into a wind and an electrostatic component, as well as on a detailed evaluation of the bond currents, shows that this remarkable electromigration phenomenon is due solely to the position-dependent wind force. © 2011 American Physical Society.
CitationZhang R, Rungger I, Sanvito S, Hou S (2011) Current-induced energy barrier suppression for electromigration from first principles. Physical Review B 84. Available: http://dx.doi.org/10.1103/PhysRevB.84.085445.
SponsorsThe authors thank T. Todorov for useful discussions and for a critical reading of our manuscript. This project was supported by the National Natural Science Foundation of China (Grant No. 61071012), China's Ministry of Education (Grant No. NCET-07-0014), the Ministry of Science and Technology of China (Grants No. 2007CB936204 and No. 2011CB933001) and the China Scholarship Council program. S.S. and I.R. acknowledge the Science Foundation Ireland (Grant No. 07/IN.1/I945). I.R. thanks the King Abdullah University of Science and Technology for financial support (ACRAB project). Calculations were performed within the Irish Centre for High-End Computing and on the Parsons cluster maintained by the Trinity Centre for High Performance Computing.
PublisherAmerican Physical Society (APS)
JournalPhysical Review B