The Channel Length Effect on the Electrical Performance of Suspended-single-wall-carbon-nanotube-based Field Effect Transistors

We report on the electrical performance of field effect transistor (FET) nanodevices based on suspended single-wall carbon nanotubes (SWCNTs) grown by our 'all-laser' synthesis process. The attractiveness of the proposed approach lies in the combination of standard microfabrication processing with the in situ 'all-laser' localized growth of SWCNTs, offering an affordable way of directly integrating SWCNTs into nanodevices. The 'all-laser' process uses the same KrF excimer laser (248 nm), first, to deposit the nanocatalyzed electrodes and, in a second step, to grow the SWCNTs in a suspended geometry, achieving thereby the lateral bridging of the electrodes. The nanocatalyzed electrodes consist of a multilayer stack sandwiching a catalyst nanolayer ( approximately 5 nm thick) composed of Co/Ni nanoparticles. The 'all-laser' grown SWCNTs ( approximately 1 nm diameter) are most often seen to self-assemble into bundles (10-20 nm diameter) and to bridge laterally the various gap lengths (in the 2-10 microm investigation range) separating adjacent electrodes. The suspended-SWCNT-based FETs were found to behave as p-type transistors, in air and at room temperature, with very high ON/OFF switching ratios (whose magnitude markedly increases as the active channel length is reduced). For the shortest gap (i.e. 2 microm), the suspended-SWCNT-based FETs exhibited not only an ON/OFF switching ratio in excess of seven orders of magnitude, but also an ON-state conductance as high as 3.26 microS. Their corresponding effective carrier mobility was estimated (at V(SD) = 100 mV) to a value of approximately 4000 cm(2) V(-1) s(-1), which is almost ten times higher than the hole mobility in single-crystal silicon at room temperature.