Comprehensive Study on High Purity Semiconducting Carbon Nanotube Extraction

Abstract

Carbon nanotubes (CNTs) are a rapidly maturing emerging technology for next-generation energy-efficient digital Very-Large-Scale-Integrated (VLSI) systems. However, a major remaining challenge facing CNT field-effect transistors (CNFETs) are metallic CNTs, causing incorrect logic functionality and increased leakage power. As no CNT synthesis technique demonstrates a reliable path toward manufacturing 99.99% semiconducting CNTs (s-CNT; required purity for VLSI systems), significant work focuses on solution-based sorting of CNTs (selectively removing metallic CNTs post-synthesis). Yet, there lacks both well-controlled comparisons carefully optimizing key processing parameters simultaneously (CNT synthesis sources, polymer additive used for selective sorting, etc.), as well as statistically significant electrical transistor characterization sample sizes to form concrete conclusions. Here, >90 000 CNFETs (totaling >90 million CNTs) are fabricated and characterized to demonstrate the following key advances: 1) systematic exploration of the impact of different combinations of CNT synthesis sources and polymer additives on the electrical performance of transistors (analyzing on-current, off-current, on off ratio, and threshold voltage) to find the best combination, 2) how the optimization and choice of the CNT source can be decoupled from that of the polymer, and 3) an optimal CNT solution that achieves >99.99% s-CNT purity using electrical measurements, meeting the requirement for VLSI systems.