High-Frequency Analysis of Carbon Nanotube Interconnects and Implications for On-Chip Inductor Design

This paper presents a rigorous investigation of high-frequency effects in carbon nanotube (CNT) interconnects and their implications for the design and performance analysis of high-quality on-chip inductors. A frequency-dependent impedance extraction method is developed for both single-walled CNT (SWCNT) and multiwalled CNT (MWCNT) bundle interconnects. The method is subsequently verified by comparing the results with those derived directly from the Maxwell's equations. Our analysis reveals for the first time that skin effect in CNT (particularly MWCNT) bundles is significantly reduced compared to that in conventional metal conductors, which makes them very attractive and promising material for high-frequency applications, including high-quality (Q) factor on-chip inductor design in high-performance RF/mixed-signal circuits. It is shown that such unique high-frequency properties of CNTs essentially arise due to their large momentum relaxation time (leading to their large kinetic inductance), which causes the skin depths to saturate with frequency and thereby limits resistance increase at high frequencies in a bundle structure. It is subsequently shown that CNT-based planar spiral inductors can achieve more than three times higher Q factor than their Cu-based counterparts without using any magnetic materials or Q factor enhancement techniques.