Rice University researchers have discovered thin films of nanotubes created with ink-jet printers offer a new way to make field-effect transistors (FET), the basic element in integrated circuits.
This is not a perfect transistor, but it is applicable in digital electronics,” Vajtai said. “There are some limitations. I doubt anyone could take a $60 ink-jet printer and print predesigned electronic circuits. But with a high-end printer, it is a fairly straightforward process and allows you to put together whatever you want.” He expects manufacturing nano-FETS in bulk would require a process more akin to silk-screening.
Though the researchers’ test FETs were relatively large — about a square millimeter — they reported that circuits could scale down to about 100 microns, about the width of a human hair, with a channel length of about 35 microns – the size of the print head. Shrinking them further might be possible with smaller print heads or pretreated hydrophilic or hydrophobic surfaces.
Vajtai said nanotube-based FETs will be good for logic-based applications that can be printed on a flexible surface but don’t need a large number of circuits. “Say you want to have a raincoat made with transistors – doing whatever a raincoat needs to do that requires electricity, such as controlling and analyzing signals from several sensors and light sources, for safety. It can be done.”
The electrical properties of random networks of single-wall carbon nanotubes (SWNTs) obtained by inkjet printing are studied. Water-based stable inks of functionalized SWNTs (carboxylic acid, amide, poly(ethylene glycol), and polyaminobenzene sulfonic acid) were prepared and applied to inkjet deposit microscopic patterns of nanotube films on lithographically defined silicon chips with a back-side gate arrangement. Source−drain transfer characteristics and gate-effect measurements confirm the important role of the chemical functional groups in the electrical behavior of carbon nanotube networks. Considerable nonlinear transport in conjunction with a high channel current on/off ratio of 70 was observed with poly(ethylene glycol)-functionalized nanotubes. The positive temperature coefficient of channel resistance shows the nonmetallic behavior of the inkjet-printed films. Other inkjet-printed field-effect transistors using carboxyl-functionalized nanotubes as source, drain, and gate electrodes, poly(ethylene glycol)-functionalized nanotubes as the channel, and poly(ethylene glycol) as the gate dielectric were also tested and characterized.