Interface Engineering of Electrical Contacts

Abstract

Highly conductive nanoscale electrical contacts suffer from strong current crowding at the contact edges, which can lead to nonuniform heat deposition; the formation of local hot spots, aggravation of electromigration; and, in the worst-case scenario, lead to thermal runaway and breakdown of the device. These effects severely affect the overall device properties, reliability, and lifetime. Devices based on thin-film junctions, nanotubes or nanowires, and two-dimensional (2D) materials are especially sensitive to current transport at electrical contacts, due to their reduced dimensions and increased geometrical confinement for current flow. Here, we demonstrate a method to mitigate current crowding, by engineering the interface layer properties and geometry. Based on a self-consistent transmission-line model, we show that the distribution of the contact current greatly depends on the properties of the interfacial layer between two contacting members. Current steering and redistribution can be realized by strategically designing the specific contact resistivity, ${\ensuremath{\rho}}_{c}$, along the contact length. For similar contact members, parabolically varying ${\ensuremath{\rho}}_{c}$ along the contact interface significantly reduces the edge-current crowding in ohmic contacts. Similarly, the nonuniform current distribution of 2D semiconductor-3D metal contacts can be decreased, and the current-transfer length can be increased by varying the Schottky barrier height along the interface. It is also found that introducing a nanometer- or subnanometer-scale thin insulating tunneling gap between contact members can greatly reduce current crowding, while maintaining a similar total contact resistance.