  The effect of phonon scattering on the intrinsic delay and cut-off frequency
of Schottky barrier carbon nanotube (CNT) FETs is examined by self-consistently
solving the Poisson equation and the Schrodinger equation using the
non-equilibrium Greens function (NEGF) formalism. Carriers are mostly scattered
by optical and zone boundary phonons beyond the beginning of the channel. We
show that the scattering has a small direct effect on the DC on-current of the
CNTFET, but it results in significant pile-up of charge and degradation of
average carrier velocity. Due to charge pile-up and random walks of carriers,
the intrinsic gate capacitance and delay significantly increase, and the
intrinsic cut-off frequency decreases. The results are important for assessing
the performance potential of CNTFETs for radio-frequency (RF) electronics and
digital electronics applications.
