On The Applicability Of Carbon Nanotubes As Interconnect In Nanoscale Integrated Circuits

Due to the feature size of VLSI continue shrinking, the process technology has gone into nanoscale (< 100 nm) region, and microelectronics has been developed into the era of nanoscale integrated circuits. In previous deep sub-micron technology, interconnect issue has arised lots of concern and become one of critical issue of the IC design. In nanoscale region, interconnect is going to encounter more limitation problems, such as the increasing of metal resistivity, degradation of thermal properties and more serious reliability issue. Hence, the research of new process, new structure and new material for interconnect are becoming more and more active and important.This work is mainly focus on one of the most popular new material– Carbon Nanotube (CNT) as the application of future interconnects in nanoscale IC. At beginning, the structure of CNT is introduced and the electrical and thermal properties of CNT are discussed. Meanwhile, the development of CNT fabrication process and its challenging are reviewed.Due to the fact that CNTs can be classified as Single-Walled CNTs (SWCNTs) or Multi-Walled CNTs (MWCNTs), this work has two parts accordingly. For SWCNT, resistance, inductance and capacitance (RLC) are discussed, especially for the unique parameters of 1-D conductor: quantuam resistance, quantum capacitance and kinetic inductance. The distributed equivalent circuit model which is compatible with existing circuit simulator has been proposed for SWCNT bundle for future interconnect application. Based on the model, the circuit performance of SWCNT interconnect has been evaluated at different interconnect levels (local, intermediate and global) and compared with mainstream Cu interconnect. It is shown that for intermediate and global interconnects, SWCNT interconnect can largely enhance the circuit performance.For MWCNTs, the equivalent circuit model has been proposed for the first time. In this model, diameter dependent of conducting channel number is considered, and therefore diameter dependent of resistance, capacitance and inductance are incorporated. Moreover, the inter-shell effect of MWCNT, such as tunneling conductance, coupling capacitance and mutual inductance are also taken into account. Based on the proposed equivalent model, circuit performance of MWCNT interconnect are analyzed and compared with Cu interconnect and SWCNT interconnect, respectively. It can be observed that for intermediate and global level, delay of MWCNT interconnect can reach as low as 15% of that of Cu interconnect, which indicate the performance is enhanced significantly. When compared to SWCNT interconnect, MWCNT could be comparable to SWCNT if SWCNT bundle is densely packed and 100% metallic; or even better than SWCNT if SWCNT bundle pack density and metallic fraction is not that high (~30%).This work has discussed comprehensively about the circuit performance of CNT as future interconnect in nanoscale IC. The proposed models and analysis results are important for future analysis and desigin of CNT interconnect. Also, it provides suggestions and guidelines for CNT fabrication efforts.