The channel length effect on the electrical performance of suspended-single-wall-carbon-nanotube-basedfield effect transistors

Abstract

We report on the electrical performance of field effect transistor (FET) nanodevices basedon suspended single-wall carbon nanotubes (SWCNTs) grown by our ‘all-laser’ synthesisprocess. The attractiveness of the proposed approach lies in the combination of standardmicrofabrication 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 depositthe nanocatalyzed electrodes and, in a second step, to grow the SWCNTs in asuspended geometry, achieving thereby the lateral bridging of the electrodes. Thenanocatalyzed electrodes consist of a multilayer stack sandwiching a catalyst nanolayer (∼5 nm thick) composed of Co/Ni nanoparticles. The ‘all-laser’ grown SWCNTs (∼1 nm diameter) are most often seen to self-assemble into bundles (10–20 nmdiameter) and to bridge laterally the various gap lengths (in the 2–10 µm investigation range) separating adjacent electrodes. The suspended-SWCNT-based FETswere found to behave as p-type transistors, in air and at room temperature, with very highON/OFF switchingratios (whose magnitude markedly increases as the active channel length is reduced). For the shortestgap (i.e. 2 µm), the suspended-SWCNT-based FETs exhibited not only anON/OFF switching ratio in excess of seven orders of magnitude, but also an ON-state conductance as highas 3.26 µS. Their corresponding effective carrier mobility was estimated (atVSD = 100 mV) to avalue of ∼4000 cm2 V−1 s−1, which is almost ten times higher than the hole mobility in single-crystal silicon at roomtemperature.