High k dielectrics for molecular transistors.
We demonstrated high performance nanotube FETs with integrated high-k gate dielectrics [A. Javey et al., Nature Materials, 2002] approaching the 60 mV/decade subthreshold swing theoretical limit for field effect devices.


Ohmic contacts.
More recently, we pushed SWNT FETs to the ballistic quantum limit by developing Pd ohmic contacts to finite length semiconducting nanotubes [A. Javey, Nature, 2003]. Pd contacts have now been used by many research groups for device demonstrations and physics studies.

Ballistic channels.
We showed quasi-ballistic transport in ultra-short nanotubes at high biases or energies, overcoming the optical phonon scattering limitation by length scaling [Javey, PRL, 2004; PNAS, 2004].

Complementary electronics.
We pushed the performance limit of both p- and n-type SWNT FETs, by making self-aligned ultra-short nanotube FETs with high k dielectrics [Javey, Nano Lett., 2004; Nano Lett., 2005].

DNA and nanotube electronics?
Single-walled carbon nanotubes (SWNTs) are advanced quasi-1D materials for future high performance electronics. SWNT field effect transistors (FETs) outperform state-of-the-art Si FETs owing to near ballistic electrical transport, chemical robustness, lack of surface dangling bonds and sustained electrical properties when integrated into realistic device structures.

For single-walled carbon nanotube (SWNT) field effect transistors, vertical scaling of high κ 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. We have shown [Y. Lu et al., JACS, 2006] 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 κ 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.

(2.2) Organic molecular electronics with nanotubes as electrodes

SWNT
Our group has used single-walled carbon nanotubes (SWNT) as quasi one-dimensional (1D) electrodes to construct organic field effect transistors (FET) with molecular scale width and channel length [P. Qi et al, JACS, 2004]. Theoretical calculation shows that the sharp quasi-1D electrode geometry introduced by SWNTs allows for more efficient switching of ultra-short organic channels compared with lithographically patterned bulk metal electrodes. The better gate electrostatics will be able to facilitate fundamental investigations of electron transport in molecules over a wide range of energies through electrostatic gating.

AFM image of a cut SWNT (diameter ~ 2 nm, gap size L measured to be ~ 6 nm after correction of the tip size effect). Right inset: AFM image of a vapor-deposited pentacene crystallite bridging a cut SWNT		Schematic drawing of a cut SWNT with a sub-10 nm gap to be used as source (S) and drain (D) electrodes to form organic FETs. The doped Si serves as a back-gate (G) and the SiO2 thickness tox=10 nm.