Electronic Structure and Contact Resistance at the Interface Between Carbon Nanotubes and Copper Pad

Due to their unique and superior mechanical and electrical properties, carbon nanotubes (CNTs) are a promising candidate as electrical interconnects in nanoscale electronics. A key element in using CNT as electrical interconnects is the full understanding of the mechanical and electrical behavior of the interface between the CNT and copper (Cu) pad. The objective of this paper is to study the electronic structure and the electrical contact resistance at the interface between the open end of a single wall CNT and a Cu pad. To accomplish this, simulation cell consisting of an open-end single wall CNT with each end connected to a Cu electrode was created. The Cu/CNT/Cu system is fully relaxed first before a potential bias is prescribed between the Cu electrodes. The first-principle quantum mechanical density functional and non-equilibrium Green’s function (NEGF) approaches are adopted to compute the transport coefficient, while the current-voltage (I-V) relation is then extracted by invoking the Landauer-Buttiker formalism. The average density of state (DOS) and local density of states (LDOS) are also calculated to obtain the electron energy distribution around Fermi level point. Our simulation results show that electrons are conducted through the Cu/CNT/Cu system. In the low voltage bias regime (0.0∼0.1 V), I-V relationship is found to be linear. At higher voltage (> 2.0 V), the I-V relationship is nonlinear. Our results also show that the electrical contact resistance at the CNT/Cu interface is ∼3.6 kΩ at 0.1 V, and ∼4.8 kΩ at 2.0 V. These results indicate that for open-end CNTs, the contact resistance at the CNT/Cu interface is at least comparable to that of solder/Cu interface.