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Nanotubes may shrink chips

IBM predicts even faster and smaller devices

SAN FRANCISCO — IBM scientists are reporting progress in a chip-making technology that is likely to ensure the shrinking of the basic digital switch at the heart of modern microchips for more than another decade.

The advance, described in the journal Nature Nanotechnology on Sunday, is based on carbon nanotubes, molecules that have long held promise as an alternative material to silicon from which to create the tiny logic gates that are used by the billions to create microprocessors and memory chips.

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IBM researchers at the T.J. Watson Research Center in Yorktown Heights, N.Y., have been able to pattern an array of carbon nanotubes on the surface of a silicon wafer and use them to build chips that are hybrids of silicon and carbon nanotubes with more than 10,000 working transistors.

Against all expectations, the silicon chip has continued to improve in both speed and capacity for the past five decades. In recent decades, however, there has been growing uncertainty over whether the technology will continue to improve. The end of the microelectronics era would inevitably stall a growing array of industries that have fed off the falling cost and increasing performance of computer chips.

Chip makers have routinely doubled the number of transistors that can be etched on the surface of silicon wafers by routinely shrinking the tiny switches that store and route the ones and zeros that are processed by digital computers. They have long since shrunk the switches to less than a wavelength of light, and they are rapidly approaching dimensions that can be measured in terms of the widths of just a few atoms.

The process has been characterized as Moore’s Law, named after Gordon Moore, the Intel cofounder, who in 1965 noted the industry was doubling the number of transistors it could build on a single chip at routine intervals of 12 to 18 months.

To continue the process, semiconductor engineers have had to consistently perfect an array of related manufacturing systems and materials that continue to perform at an ever tinier scale.

‘These devices outperformed any other switches made from any other material.’

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In recent years, while chip makers have continued to double the number of transistors on microprocessors and memory chips, their performance, measured as ‘‘clock speed,’’ has largely stalled. This has forced the computer industry to change its design and begin building more parallel computers. Today, even smartphone microprocessors come with as many as four processors, or ‘‘cores,’’ which are used to break up tasks so they can be processed simultaneously.

IBM scientists said they believe that once they have perfected the use of carbon nanotubes sometime after the end of this decade, it will be possible to dramatically raise the speed of future chips as well as dramatically increase the number of transistors.

This year, IBM researchers published a separate paper describing the speedup made possible by the new material.

‘‘These devices outperformed any other switches made from any other material,’’ said Supratik Guha, director of physical sciences at IBM Research. ‘‘We had suspected this all along, and our device physicists had simulated this, and they showed that we would see a factor of five or more performance improvement over conventional silicon devices.’’

Carbon nanotubes are essentially single sheets of carbon rolled into nanoscale tubes. In the Nature Nanotechnology paper, the IBM researchers described how they placed ultrasmall rectangles of the material in regular arrays by putting them in a soapy mixture that makes them soluble in water. They used a process they described as ‘‘chemical self-assembly’’ to create the patterned array in which the nanotubes stick in some areas of the surface while other ­areas are left untouched.

Perfecting the process will require a more highly purified form of the carbon nanotube material.

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