A small-scale solution with a large-scale impact

Aug 27, 2012 by Angela Herring
A small-scale solution with a large-scale impact
A com­puter chip using the molyb­denum disul­fide inverter. Photo: Brooks Canaday

(Phys.org)—Microchips are per­va­sive in today's high-​​tech society, playing inte­gral roles in the inner work­ings of your cell phone to your Keurig coffee machine.

A pro­cessing tech­nology called , or com­ple­men­tary metal–oxide–semiconductor, made microchips eco­nom­i­cally fea­sible in the 1980s, said Siva­sub­ra­manian Somu, a research sci­en­tist in Northeastern's Center for High-​​rate Nanoman­u­fac­turing.

A crit­ical ele­ment in any microchip is some­thing called an inverter—an elec­tronic com­po­nent that spits out zeros when you give it ones, and vice versa. "A tran­sistor [the basic ele­ment in an inverter] is a simple, extremely fast switch," Somu explained. "You can turn it on and off by elec­tric signals."

In the early days of com­puter tech­nology, mechan­ical switches were used for com­pu­ta­tional oper­a­tions. "You cannot achieve fast com­pu­ta­tions using mechan­ical switches," Somu said. So CMOS, which used elec­tric sig­nals to turn the switches on and off, rep­re­sented a sig­nif­i­cant advance in the field.

But despite its rel­a­tive economy, a CMOS fab­ri­ca­tion plant still costs about $50 bil­lion, according to Somu. "We needed an alter­na­tive, cost-​​effective solu­tion that still can com­pete with CMOS at the foundry level," he said.

CHN's pro­pri­etary "directed-​​assembly" approach is that alter­na­tive solu­tion. Instead of requiring sev­eral fab­ri­ca­tion steps of adding and removing mate­rial, as in the case of CMOS, directed assembly is an additive-​​only process that can be done at room tem­per­a­ture and pres­sure. A fab­ri­ca­tion facility based on this tech­nology, Somu said, could be built for as little as $25 million.

A small-scale solution with a large-scale impact
A custom probe sta­tion that varies tem­per­a­ture and atmos­pheric pres­sure to mea­sure the elec­trical prop­er­ties of mate­rials at the Center for High-​​rate Nanoman­u­fac­turing. Photo: Brooks Canaday

This cost sav­ings would make nan­otech­nology acces­sible to mil­lions of new inno­va­tors and entre­pre­neurs, unleashing a wave of cre­ativity the same way the PC did for com­puting, said Ahmed Bus­naina, the William Lin­coln Smith Pro­fessor and Director of the NSF Center for High-​​rate Nanomanufacturing.

But cre­ating a nano­sized inverter is easier said than done, added Jun Huang, a post­doc­toral research sci­en­tist in the center. Researchers have using mate­rials like graphene and carbon nan­otubes for cre­ating inverters, but none of these has worked well on its own. Cre­ating a nano­sized inverter made up of dif­ferent nano­ma­te­rials with excel­lent prop­er­ties, Huang said, can result in excel­lent com­pli­men­tary transistors.

Using the directed-​​assembly process, the team cre­ated an effec­tive com­pli­men­tary inverter using Molyb­denum disul­fide and carbon nan­otubes. "At the nanolevel," said Huang, "molyb­denum disul­fide occurs in thin, nanometer-​​thick sheets." At this scale, he noted, the mate­rial begins to demon­strate tran­sistor char­ac­ter­is­tics crit­ical to the con­struc­tion of a good inverter.

The suc­cess rep­re­sents a step toward CHN's ulti­mate goal of enabling small– and medium-​​sized busi­nesses to develop new, -​​based tech­nolo­gies. The results of their research were reported in a recent article in the journal Nanotechnology.

Explore further: Scientists craft atomically seamless, thinnest-possible semiconductor junctions

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