  We performed a comprehensive scaling study of Schottky barrier carbon
nanotube transistors using self-consistent, atomistic scale simulations. We
restrict our attention to Schottky barrier carbon nanotube FETs whose metal
source/drain is attached to an intrinsic carbon nanotube channel. Ambipolar
conduction is found to be an important factor that must be carefully considered
in device design, especially when the gate oxide is thin. The channel length
scaling limit imposed by source-drain tunneling is found to be between 5nm and
10nm, depending on the off-current specification. Using a large diameter tube
increases the on-current, but it also increases the leakage current. Our study
of gate dielectric scaling shows that the charge on the nanotube can play an
important role above threshold.
