Evolution of local temperature in Au nanowires during feedback-controlled electromigration observed by atomic force microscopy

Abstract

Feedback-controlled electromigration (FCE) has been developed to enable more reproducible fabrication of nanoscale gaps between two metallic electrodes. However, there remains considerable uncertainty about some aspects of the FCE process. In this study, electromigration (EM)-induced mass transport in Au nanowires during the application of a voltage feedback technique was directly observed by in situ atomic force microscopy (AFM). The measured results unambiguously revealed a decrease in the cross-sectional area of the nanoconstriction early in the FCE process. In addition, the local temperature in the biased nanoconstriction was estimated using the diffusive heat transport relation. During FCE, the onset of EM occurred at local temperatures ranging from 420 K to 557 K in a room-temperature environment when the current density was held constant at 108 A/cm2. We found that the local temperature at the onset of EM increased in our results when the Joule heating power in the nanoconstriction was not constant. In these cases, the experimental procedure enables the local temperature to rise in a controlled manner. Our results imply that the controlled EM proceeded without causing the nanowires to melt due to Joule heating. The in situ AFM results also enabled the changes in the electrical properties to be correlated directly with the physical modifications occurring in the Au nanowires during FCE.