Carbon nanotube and oxide nanobelt FETs: fabrication, characterization and applications

High-performance field effect transistors (FETs) based on single-wall carbon nanotubes (SWNTs) and oxide nanobelts were fabricated and characterized. The SWNT-FETs were constructed via molecular template-directed assembly of HiPCO tubes onto pre-patterned metal electrodes on a Si/SiO$_{2}$ substrate. The devices exhibit operating characteristics comparable to state-of-the-art CNT FETs, and the process is amenable to large-scale functional CNT circuit assembly. Importantly, the integration of hydrophobic self-assembled organic monolayers in the device structure eliminates the primary source of gating hysteresis in SWNT-FETs, which leads to hysteresis-free FET operation while exposing unmodified nanotube surfaces to ambient air$^{[1]}$. Individual oxide (SnO$_{2}$ and ZnO) nanobelt FETs with multi-terminal contacts were fabricated via conventional lithography. Simultaneous two-terminal and four-terminal measurements enabled direct correlation of the FET characteristics with the nature of the contacts. Low-resistance ohmic contacts on the nanobelts result in high-performance n-channel depletion mode FETs with well-defined linear and saturation regimes, and ``on/off'' ratio as high as 10$^{7}$ at ambient conditions$^{[2]}$. Intrinsic values of the carrier concentration and effective mobility for the nanobelts were consequently obtained. Channel-limited SnO$_{2}$ nanobelt devices show significant modification of the FET characteristics when exposed to gas flows containing 0.2-2{\%} H$_{2}$ at room temperature. The gas sensitivity and response were carefully evaluated$^{[3]}$. The effort to utilize the channel-limited nanobelt FETs for protein detection will be discussed. $^{[1] }$S.A. McGill et al., APL \textbf{89}, 163123 (2006). $^{[2] }$Y. Cheng et al., APL \textbf{89}, 093114 (2006). $^{[3] }$L.L. Fields et al., APL \textbf{88}, 263102 (2006).