This paper reports the radio frequency (RF) and linearity performance of transistors using high-purity semiconducting carbon nanotubes. High-density, uniform semiconducting nanotube networks are deposited at wafer scale using our APTES-assisted nanotube deposition technique, and RF transistors with channel lengths down to 500 nm are fabricated. We report on transistors exhibiting a cutoff frequency (f(t)) of 5 GHz and with maximum oscillation frequency (f(max)) of 1.5 GHz. Besides the cutoff frequency, the other important figure of merit for the RF transistors is the device linearity. For the first time, we report carbon nanotube RF transistor linearity metrics up to 1 GHz. Without the use of active probes to provide the high impedance termination, the measurement bandwidth is therefore not limited, and the linearity measurements can be conducted at the frequencies where the transistors are intended to be operating. We conclude that semiconducting nanotube-based transistors are potentially promising building blocks for highly linear RF electronics and circuit applications.
Carbon nanotube RF transistors are predicted to offer good performance and high linearity when operated in the ballistic transport and quantum capacitance regime; however, realization of such transistors has been very challenging. In this paper, we introduce a self-aligned fabrication method for carbon nanotube RF transistors, which incorporate a T-shaped (mushroom-shaped) aluminum gate, with oxidized aluminum as the gate dielectric. In this way, the channel length can be scaled down to 140 nm, which enables quasi-ballistic transport, and the gate dielectric is reduced to 2-3 nm aluminum oxide, leading to quasi-quantum capacitance operation. A current-gain cutoff frequency (f(t)) up to 23 GHz and a maximum oscillation frequency (f(max)) of 10 GHz are demonstrated. Furthermore, the linearity properties of nanotube transistors are characterized by using the 1 dB compression point measurement with positive power gain for the first time, to our knowledge. Our work reveals the importance and potential of separated semiconducting nanotubes for various RF applications.
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