  For single-walled carbon nanotube (SWNT) field effect transistors, vertical
scaling of high k dielectrics by atomic layer deposition (ALD) currently stands
at ~8nm with subthreshold swing S~70-90 mV/decade at room temperature. ALD on
as-grown pristine SWNTs is incapable of producing a uniform and conformal
dielectric layer due to the lack of functional groups on nanotubes and that
nucleation of an oxide dielectric layer in the ALD process hinges upon covalent
chemisorption on reactive groups on surfaces. Here, we show that by
non-covalent functionalization of SWNTs with ploy-T DNA molecules (dT40-DNA),
one can impart functional groups of sufficient density and stability for
uniform and conformal ALD of high k dielectrics on SWNTs with thickness down to
2-3nm. This enables approaching the ultimate vertical scaling limit of nanotube
FETs and reliably achieving S ~ 60mV/decade at room temperature, and
S~50mV/decade in band to band tunneling regime of ambipolar transport. We have
also carried out microscopy investigations to understand ALD processes on SWNTs
with and without DNA functionalization.
