  The band-to-band tunneling transistors have some performance advantages over
the conventional MOSFETs due to the <60mV/dec sub-threshold slope. In this
paper, carbon nanotubes are used as a model channel material to address issues
that we believe will apply to BTBT FETs vs. MOSFETs more generally. We use
pz-orbital tight-binding Hamiltonian and the non-equilibrium Green function
(NEGF) formalism for rigorous treatment of dissipative quantum transport. A
device level comparison of p-i-n TFETs and n-i-n MOSFETs in both ballistic and
dissipative cases has been performed previously. In this paper, the possibility
of using p-i-n TFETs in ultra-low power sub-threshold logic circuits is
investigated using a rigorous numerical simulator. The results show that, in
sub-threshold circuit operation, the p-i-n TFETs have better DC
characteristics, and can deliver ~15x higher performance at the iso-P_LEAKAGE,
iso-VDD conditions. Because p-i-n TFETs can operate at lower VDD than n-i-n
MOSFETs, they can deliver ~3x higher performance at the same power
(P_OPERATION). This results in ~3x energy reduction under iso-delay conditions.
Therefore the p-i-n TFETs are more suitable for sub-threshold logic operation.
