The Nanotube Computer

By David Rotman   March 2002

The nano future is emerging through the haze of hype: the road to terabit memory and cheap flat-screen displays will be paved with carbon nanotubes.

In the hype-filled world of nanotechnology, Phaedon Avouris, head of IBM Research’s nanoscience and technology group, has a reputation as a meticulous and somewhat skeptical scientist. By his own description, he is one of those researchers whom reporters call to get a “realistic assessment” of the latest nanotech breakthrough. These days, though, the IBM chemist sounds uncharacteristically upbeat.

The reason for his excitement can be seen in a microscopic image recently produced in his lab. It shows a thin thread draped over several thick gold electrodes. What is not so apparent is that the thread, a single carbon nanotube, has been modified and positioned so that it forms two types of transistors, each a few nanometers (billionths of a meter) in diameter— a hundred times smaller than the transistors now found on computer chips. What’s more, the nanotube transistors work together as a logic gate, the fundamental computer component responsible for selectively routing electrical signals, transforming them into meaningful ones and zeroes.

The IBM device is one of the first examples of electronic circuitry constructed out of individual molecules. And while it’s merely a crude laboratory demonstration, its successful fabrication is nevertheless a further tantalizing clue that carbon nanotubes could one day replace silicon crystals as the building blocks for ultrafast, ultrasmall computers. More measurements are needed, says Avouris, “but our current results show, after taking into account difference in size, nanotube transistors show a performance superior to that of state-of-the-art silicon transistors.”

Indeed, carbon nanotubes are, in theory at least, the ideal material for building tomorrow’s nanoelectronics. And now, a little more than 10 years after their discovery, nanotubes seem ready to make the transition from exotic laboratory wonders to materials useful in actual technologies. Prototypes of nanotube devices are being tested in everything from full-color flat-panel TV screens to ultrabright outdoor lighting to a simpler, smaller x-ray machine; consumers could be shopping for a flat-screen TV that uses nanotubes as early as Christmas 2003.

But it is in computer memory and logic that nanotubes could have their greatest impact. Microelectronics now use silicon transistors with features as small as 130 nanometers across, which means that Intel can squeeze some 42 million of these transistors onto its Pentium 4 chip. However, it’s getting harder—and far more expensive—to continue to shrink silicon devices. Using nanotubes or related materials called nanowires as tiny electronic switches would allow computer designers to cram billions of devices onto a chip. If these molecular transistors work—and that is still a big if—replacing silicon will likely take years. But the ambition, says Charles Lieber, a Harvard University chemist, is to build electronics with performance “orders of magnitude beyond silicon. We’re trying to break with what is being done, to really change things.”