2.8 CNTs in Electronics

The one-dimensional nature of CNTs severely reduces the phase space for scattering, allowing CNTs to realize maximum possible bulk mobility of this material. The low scattering probability and high mobility are responsible for high on-current of CNT transistors. Furthermore, the chemical stability and perfection of the CNT structure suggests that the carrier mobility at high gate fields may not be affected by processing and roughness scattering as in the conventional semiconductor channel. Similarly, low scattering together with the strong chemical bonding and high thermal conductivity allows metallic CNTs to withstand extremely high current densities (up to $ \sim\mathrm{10^9~A/cm^2}$).

Electrostatics is improved in these devices as well. The fact that there are no dangling bond states at the surface of CNTs allows for a much wider choice of gate insulators other than conventional $ \mathrm{SiO_2}$. This improved gate control without any additional gate leakage becomes very important in scaled devices with effective $ \mathrm{SiO_2}$ thickness below $ \mathrm{1~nm}$. Also, the strong one-dimensional electron confinement and full depletion in the nanometer-scale diameter of the SW-CNTs (typically $ 1-2~\mathrm{nm}$) should lead to a suppression of short-channel effects in transistors [5].

The combined impact of transport and electrostatic benefits together with the fact that semiconducting CNTs are, unlike silicon, direct-gap materials, suggest applications in opto-electronics as well [6,7]. As far as integration is concerned, semiconducting CNTs benefit from their band structure which exhibits essentially the same effective mass for electrons and holes. This should enable similar mobilities and performance of n-type and p-type transistors which is necessary for a complementary metal-oxide semiconductor (CMOS)-like technology. Finally, since CNTs can be both metallic and semiconducting, an all-CNT electronics can be envisioned. In this case, metallic CNTs could act as high current carrying local interconnects [62], while semiconducting CNTs would form the active devices. The most important appeal of this approach is an ability to fabricate one of the critical device dimensions (the CNT diameter) reproducibly using synthetic chemistry.

M. Pourfath: Numerical Study of Quantum Transport in Carbon Nanotube-Based Transistors