Carbon nanotubes (CNTs) have been considered a preferred channel material for constructing high-performance radio frequency (RF) transistors with outstanding current gain cutoff frequency (fT) and power gain cutoff frequency (fmax) but the highest reported fmax is only 70 GHz. Here, we explore how good RF transistors based on solution-derived randomly oriented semiconducting CNT films, which are the most mature CNT materials for scalable fabrication of transistors and integrated circuits, can be achieved. Owing to the significantly reduced number of CNT/CNT junctions obtained by scaling the channel length down to below 100 nm, we realized RF field-effect transistors (FETs) with maximum transconductance Gm up to 0.38 mS/μm, which is the record among CNT-based RF FETs. After de-embedding the pad-induced capacitances and resistances, the CNT FETs with different gate lengths (Lg) exhibit fT as high as 103 GHz (intrinsically 281 GHz) or fmax up to 107 GHz (intrinsically 190 GHz), which are the records among CNT-based RF FETs. In particular, the CNT FETs with an Lg of 50 nm present pad de-embedding fT of 86 GHz and fmax of 85 GHz, and represent the best CNT RF transistor in terms of comprehensive performance to date. To demonstrate the actual high-speed and scalable fabrication of our CNT RF FETs, we fabricated CNT FET-based five-stage ring oscillators with oscillation frequencies above 5 GHz.
Keywords: carbon nanotube; cutoff frequency; maximum oscillation frequency; radio frequency; randomly oriented film.