Terahertz metal-oxide-semiconductor transistors based on aligned carbon nanotube arrays

The development of wireless communications is driving the need for compact radiofrequency (RF) devices with up to terahertz (THz) frequency and fabrication processes compatible with that of complementary-metal-oxide-semiconductor (CMOS) transistors. Aligned carbon nanotube (A-CNT) film is a promising candidate semiconductor that can be used to build both CMOS field-effect transistors (FETs) for digital integrated circuits (ICs) and radiofrequency (RF) transistors with frequencies beyond 1 THz for analogue ICs. Herein, we demonstrate the first MOS FET with a cut-off frequency beyond 1 THz on a high-quality A-CNT array film, and with a carrier mobility of 2,000 cm² V^{− 1} s^{− 1} and better scaling characteristics than all semiconductors, including GaAs and InP. The fabricated CNT MOS FETs present a record performance that includes an on-state current of 3.02 mA µm^{− 1}, a peak transconductance of 2.17 mS µm^{− 1} at a bias of − 1 V, and a saturation velocity of 3.5 × 10⁷ cm s^{− 1}. Through optimising device structure and fabrication process, in particular the introduction of a Y-gate, a 35 nm-gate length A-CNT MOS FET is fabricated that shows extrinsic current-gain/power-gain and cut-off frequencies of up to 551 GHz/1024 GHz, representing the fastest MOS FET for RF applications. Furthermore, CNT-based mmWave band (30 GHz) RF amplifiers are demonstrated with a high gain of 21.4 dB.