All-around contact for carbon nanotube field-effect transistors made by ac dielectrophoresis

Abstract

Carbon nanotube field-effect transistors (CNFETs) are fabricated by depositing one bundle of single-walled carbon nanotubes (SWNTs) per device between a pair of predefined Pd electrodes using ac dielectrophoresis. By repeating the process for the formation of the Pd electrodes after the bundle deposition, all-around Pd contacts are made to the SWNT bundles. After the formation of all-around contact, the CNFETs with only semiconducting SWNTs in the bundles retain a strong gate modulation with a high ratio of on to off current Ion∕Ioff⩾106. For the CNFETs with at least one metallic SWNT in the bundles, their gate modulation disappears and carbon nanotube resistors (CNRs) are obtained. The on current Ion of CNFETs is found to be sensitive to the process for the formation of all-around contact. In contrast, the two-probe resistance of CNRs is consistently reduced after the all-around contacts. The electrical measurements also indicate the presence of an interlayer residing at the SWNT/Pd contacts.