Physical insights into the operation of a 1-nm gate length transistor based on MoS2 with metallic carbon nanotube gate

Low-dimensional materials such as layered semiconductors or carbon nanotubes (CNTs) have been attracting increasing attention in the last few decades due to their inherent scaling properties, which become fundamental to sustain the scaling in electronic devices. Inspired by recent experimental results [Desai et al., Science 354, 99 (2016)], in this work we examined the ultimate performance of MoS2-channel Field Effect Transistors with a gate length of 1 nm by means of quantum transport simulations based on the Poisson equation and non-equilibrium Green's function formalism. We considered uniformly scaled devices, with channel lengths ranging from 5 to 20 nm controlled by a cylindrical gate with a diameter of 1 nm, as would be required in realistic integrated circuits. Moreover, we also evaluated the effect of the finite density of states of a carbon nanotube gate on the loss of device performance. We noticed that the sub-threshold swing for all short-channel structures was greater than the ideal 60 mV per decade limit of thermionic devices, and we attributed this to the presence of tunneling currents and gate-drain interactions. We tailored the transistor architecture in order to improve the gate control. We concluded that the limited CNT-channel capacitive coupling poses severe limitations on the operation and thus exploitation of the device.