Carbon Nanotube Vias: Does Ballistic Electron–Phonon Transport Imply Improved Performance and Reliability?

This paper investigates the electron and phonon transport and their implications for performance and reliability of single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (DWCNT), and multiwalled carbon nanotube (MWCNT) vias-possibly the most imminent application of carbon nanotube (CNT)-based components in very large scale integration chips. Accurate resistance and thermal conductance models are provided for isolated CNTs, as well as bundles of these, based on detailed electrical and thermal transport physics in the submicrometer regime. It is found that although CNT vias are both electrically and thermally in the ballistic regime, their electrical and thermal performance still cannot match that of Cu via. While the large resistance of CNT vias may not be a significant concern for local interconnects, the resistance must be minimized to avoid degradation of global interconnect performance. Furthermore, detailed 3-D electrothermal simulations indicate that Joule heating and thermal contact resistance between CNTs and metal can be a major bottleneck in extracting the maximum thermal performance from ballistic CNT bundle vias. From a processing perspective, we show that the applicability of MWCNT vias, which are currently being fabricated, is severely limited by their large thermal and electrical resistance. For SWCNT- and DWCNT-based vias, small-diameter CNTs with dense packing as well as good thermal and electrical contact between CNT and metal are needed.