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, first described in the journal Nature Nanotechnology on Sunday, is based on carbon nanotubes, exotic molecules that have long held out promise as an alternative material to silicon from which to create the tiny logic gates that are now used by the billions to create microprocessors and memory chips.
The IBM researchers at the TJ WatsonResearch Center in Yorktown Heights, NY, 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 last 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 co-founder, who in 1965 noted that 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.
The IBM advance is significant, scientists said, because the chip-making industry has not yet found a way forward beyond the next two or three generations of silicon.
"This is terrific. I'm really excited about this," said Subhasish Mitra, a Stanford Universityelectrical engineering professor who specializes in carbon nanotube materials. The promise of the new material, he said, is that not only will carbon nanotubes allow chip makers to build smaller transistors, but it is likely they will turn off and on more quickly as well.
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 believed 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 one of three promising technologies that engineers hope will be perfected in time to keep the industry on its Moore's Law pace. Graphene is being explored, as well as a variant of the standard silicon transistor, which is known as a tunneling field effect transistor.
However, Guha said that carbon nanotube materials had more promising performance characteristics and that IBM physicists and chemists had perfected a range of "tricks" to make the materials easier to make.
Carbon nanotubes are essentially single sheets of carbon rolled into nanoscale tubes. In the Nature Nanotechnology paper, the IBM researchers described how they were able to place ultrasmall rectangles of the material in regular arrays by placing 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. Less pure forms are metallic and are not good semiconductors, Guha said.
He said that Bell Labs scientists figured out ways to purify germanium, a metal in the carbon group, chemically similar to silicon, in the 1940s to make the first transistors, and he was confident that IBM scientists would be able to make 99.99 per cent pure carbon nanotubes in the future.