  The scaling behaviors of graphene nanoribbon (GNR) Schottky barrier
field-effect transistors (SBFETs) are studied by solving the non-equilibrium
Green's function (NEGF) transport equation in an atomistic basis set
self-consistently with a three-dimensional Poisson equation. The armchair edge
GNR channel shares similarities with a zigzag CNT, but it has a different
geometry and quantum confinement boundary condition in the transverse
direction. The results indicate that the I-V characteristics are ambipolar and
strongly depend on the GNR width because the bandgap of the GNR is
approximately inversely proportional to its width, which agrees with recent
experiments. A multiple gate geometry improves immunity to short channel
effects, but it offers smaller improvement than it does for Si MOSFETs in terms
of the on-current and transconductance. Reducing the oxide thickness is more
useful for improving transistor performance than using a high-k gate insulator.
Significant increase of the minimal leakage current is observed when the
channel length is scaled below 10nm because the small effective mass
facilitates strong source-drain tunneling. The GNRFET, therefore, does not
promise extending the ultimate scaling limit of Si MOSFETs. The intrinsic
switching speed of a GNR SBFET, however, is several times faster than that of
Si MOSFETs, which could lead to promising high speed electronics applications,
where the large leakage of GNR SBFETs is of less concern.
