Multiwall carbon-nanotube interconnects: radial effects on physical models and resistance calculations for various metal substrates

Based on a model with singular attractive potential of equidistant conductive cylinders, we illustrate an approach to calculate the electron spectrum of metallic multiwall carbon nanotubes (MW CNT) with an arbitrary number of coaxial layers. We compute the number of electrically active channels, Nch, in the ideal case when all MW CNT shells are contacted to the electrodes, starting from the one-electron spectrum. The dependence of Nch on the temperature and on both the innermost and outermost shells radii allows us to discuss the potential performances of MW CNT interconnects, affecting the power dissipation of integrated circuits. Our description improves over the isolated shells model, where band structures remain unaffected from each other. It turns out that, for a small innermost radius MW CNT, when all the shell are contacted to the electrodes, the presence of a geometrical potential can be quite relevant. At the same time, we prove the relevance of the inter-shell in determining Nch, for an outermost shell having hundreds of nanometers radius. We then turn our attention to the junctions of carbon nanotubes with contacting metallic elements of a nanocircuit, carrying out numerical simulations on the contacts resistance, using multiple scattering theory and the effective media cluster approach. Calculations for different multiwalled nanotube-metal contacts yield quantitatively realistic results, from several to hundreds kOhm, depending on nanotube chirality, diameter and thickness. As an indicator of possible ‘radial current’ losses the inter-wall transparency coefficient for MW CNT has been also simulated.