Nanotube chips draw near

By Eric Smalley, Technology Research News

Carbon nanotubes are all the rage in research circles because they are versatile and very small. But before these rolled-up sheets of carbon atoms can take the rest of the world by storm researchers have to make millions of them at a time in orderly arrays and connect them to form useful devices.

Carbon nanotubes usually form in a jumble, like a pile of cooked spaghetti. The challenge is to get them to form in the right places, and grow straight and in the right direction.

Researchers at Stanford University have coaxed massive arrays of single-walled carbon nanotubes to form on specific sites on the 4-inch silicon wafers used to make computer chips. Growing nanotubes in an orderly fashion on silicon wafers makes it possible for manufacturers to use existing chipmaking technology to connect the nanotubes into circuits.

The technique could eventually be used to produce massive transistor arrays for computer processors, memory chips and chemical and biological sensors, said Hongjie Dai, an assistant professor of chemistry at Stanford University. "Full wafer growth enables scalability of nanotube devices," he said.

To make the nanotubes grow on a wafer, the researchers used photolithography, an etching method that employs light and chemicals, to put an array of 10 to 100 million microscopic dots on the silicon wafer. The dots, which are as small as one micron in diameter, served as catalysts to initiate the growth of carbon nanotubes. A micron is one thousandth of a millimeter; a red blood cell measures 5 microns in diameter. The researchers then exposed the wafer to a hot vapor containing carbon. The carbon atoms condensed to form nanotubes and began their growth from the catalyst dots.

The researchers used electric fields to orient the nanotubes as they grew, said Dai. The nanotubes acted like microscopic magnets that were oriented with electric field.

One, two or three single-walled nanotubes grew from each dot, according to Dai. The nanotubes ranged from 1 to 3 nanometers in diameter and grew as long as 10,000 nanometers, which is about twice as long as a red blood cell. A nanometer is one millionth of a millimeter and one-thousandth of a micron.

The chemistry that yields the nanotubes is independent of the size of the catalyst islands, and the technique could theoretically produce a nanotube for every 100 square nanometers of surface area on a wafer, or about 800 million on a 4-inch wafer, said Dai.

The researchers' next step is using standard chip-making techniques to place metal contacts over the nanotubes to connect them into circuits, said Dai. The patterned nanotube growth technique could find using practical applications in 1 to 5 years, said Dai.

Dai's research colleagues were Nathan Franklin, Yiming Li, Robert Chen and Ali Javey of Stanford University. They published their research in the December 31, 2001 issue of the journal Applied Physics Letters. The research was funded by the Defense Advanced Research Projects Agency (DARPA).

Timeline:   1-5 years
Funding:   Government
TRN Categories:   Materials Science and Engineering; Nanotechnology; Integrated Circuits
Story Type:   News
Related Elements:  Technical paper, "Patterned growth of single-walled carbon nanotubes on full 4-inch wafers," Applied Physics Letters, December 31, 2001; "Electric-field-directed growth of aligned single-walled carbon nanotubes," Applied Physics Letters, November 5, 2001


February 20, 2002

Page One

DNA map IDs diseases

Real birds change virtual evolution

Material turns infrared to green

Nanotube chips draw near

Chip provides more bang


Research News Roundup
Research Watch blog

View from the High Ground Q&A
How It Works

RSS Feeds:
News  | Blog  | Books 

Ad links:
Buy an ad link


Ad links: Clear History

Buy an ad link

Home     Archive     Resources    Feeds     Offline Publications     Glossary
TRN Finder     Research Dir.    Events Dir.      Researchers     Bookshelf
   Contribute      Under Development     T-shirts etc.     Classifieds
Forum    Comments    Feedback     About TRN

© Copyright Technology Research News, LLC 2000-2006. All rights reserved.