Performance analysis of center to center separation between adjacent tubes of Single-Walled Carbon Nanotubes bundle as VLSI Interconnects

Abstract

The work in this report presents the application of Carbon nanotubes (CNTs) as a VLSI interconnect and its superiority over copper interconnect at 32, 22 and 16 nm technology nodes. CNTs are the promising candidates for the future interconnects and it is always used in the bundle form because the resistance offered by an isolated CNT is very high. The advantage of using carbon nanotubes as a bundle form is that the effective resistance get divided by number of CNTs in a bundle and as a result of this, the resistance decreases. The impedance parameters of a CNT bundle depend on the number of CNTs in a bundle. CNTs can outperform copper at the intermediate and global interconnect level. The SWCNT bundle is most desirable form of CNT based interconnect provided all constituent CNTs of the bundle are metallic. All the impedance parameters have been calculated by writing the script in MATLAB. It has been observed that all the impedance parameters are directly proportional to the length of interconnect. It is also observed that the resistance and inductance of interconnect increases with the decrease in technology node whereas it is reverse for capacitance. Further, the effect of center to center separation of adjacent tubes have been analyzed. A mathematical model is presented which include the effect of center to center shell distance for different technology nodes. The effect of separation of adjacent tubes in a SWCNT bundle plays an important role in the interconnect delay and power dissipation. The delay increases with an increase in the separation between adjacent tubes for the entire range of length values and tube diameters but the opposite is true for power dissipation i.e power dissipation decreases with increase in separation. Furthermore, by using equivalent single conductor model, the propagation delay and power dissipation are simulated using spice simulation tool. The Optimum CMOS driver size and effect of repeaters on a SWCNT interconnect has been analyzed. It is shown in the results that the influence of center to center separation of adjacent tubes on a SWCNT bundle has a considerable impact on the propagation delay and power dissipation. It is also observed that as the bundle density is decreased the corresponding delay increases but at the same time power dissipation decreases.