Current technology-design optimization methodology focuses first on front-end devices and logic gates and then addresses back-end interconnects. But, such approach is no longer feasible for sub-nanometer technologies. Here, we present a circuit-level study where both devices and interconnects are co-optimized to improve energy efficiency. We investigate advanced CMOS technology with 7 nm FinFET devices, and Cu interconnects with various aspect ratios from 3, 5 to 10. Further, we explore the advantages of carbon nanotube (CNT) based circuits with CNT field-effect devices and interconnects. CNT technology can achieve better energy-delay-product with co-exploring front- and back-end co-optimization and paving the way for an intelligent circuit-/system-level design and technology co-optimization.