The feasibility of Carbon Nanotubes for power delivery in 3-D Integrated Circuits

Increased power density and package asymmetry pose challenges in designing power delivery networks for 3-D Integrated Circuits (ICs). The increased resistivity of Cu wires due to scaling has shifted attention to alternate interconnect technologies. Continued and significant innovations in CNT manufacturing at CMOS-compatible temperatures with quality low-resistive contacts promise to enable the use of CNT as a replacement. We investigate in this paper the feasibility of using CNTs for power delivery in 3-D ICs. We evaluate the use of CNTs as Through-Silicon Vias (TSVs) and as wiring for global power delivery grids, fabricated on interposer dies. We assume the CNT interconnect has a mix of single- and multi-walled CNTs with 30% metallic nanotubes. We design a 3-D system-level comparative framework that utilizes select traces from SPEC benchmarks to evaluate improvements of CNTs over Cu. Our results emphasize how CNTs can significantly improve power delivery for 3-D integrated circuits. Using CNTs for on-chip power grid and for TSVs reduces the number of TSVs by 71% when compared to a Cu implementation. For the same substrate area dedicated to power-TSVs, CNTs improve the maximum and average IR drop by 98% and 40%, respectively. Improvements in the Ldi/dt drop are 47% and 18%, respectively.