A Novel Fabrication Method for Pristine Suspended Carbon Nanotube Devices*

A simple and scalable method has been developed to fabricate suspended carbon nanotube (CNT) field effect transistors using as-grown CNTs without subsequent chemical processing.\footnote{\textit{V. K. Sangwan} et al, APL \textbf{93}, 113112 (2008)} A printing process is used to transfer CVD-grown CNTs onto specially configured electrode (Au) sets fabricated on SiO$_{2}$. The versatility of the technique is demonstrated by controlling the number of suspended CNTs per device, and by re-using the same electrode set multiple times to produce the desired device characteristics. The quality of suspended CNTs is characterized by electrical transport as well as 1/f noise measurements. Standard resist-processed CNTs on SiO$_{2}$ substrates show p-type behavior and strong hysteresis associated with doping by the SiO$_{2}$ surface and charge trapping in the SiO$_{2}$, respectively. In contrast, suspended CNTs show ambipolar behavior with negligible hysteresis. Low frequency noise measurements on suspended CNT show 1$/f$ behavior with Hooge's constant 2.6 x 10$^{-3}$, around 20 times less than that of CNTs lying on SiO$_{2}$, consistent with reduced effect of the SiO$_{2}$ charge traps, responsible for the bulk of the noise in CNTs on SiO$_{2}$.