World's first carbon-nanotube computer build

Scientists, led by an Indian-origin researcher, have developed the world's first computer built entirely with carbon nanotubes, opening the door to a new generation of faster-running digital devices.
Carbon nanotubes - a semiconductor material - has the potential to launch a new generation of electronic devices that run faster, while using less energy, than those made from silicon chips, researchers said.
This unprecedented feat culminates years of efforts by scientists around the world to harness this promising but quirky material.
"People have been talking about a new era of carbon nanotube electronics moving beyond silicon," said Subhasish Mitra, an electrical engineer and computer scientist at Stanford University.

"But there have been few demonstrations of complete digital systems using this exciting technology. Here is the proof," said Mitra, lead author of the study.
CNTs are long chains of carbon atoms that are extremely efficient at conducting and controlling electricity. They are so thin - thousands of CNTs could fit side by side in a human hair - that it takes very little energy to switch them off, according to Wong, a co-author of the paper.

Over time, researchers have devised tricks to grow 99.5 per cent of CNTs in straight lines. But with billions of nanotubes on a chip, even a tiny degree of misaligned tubes could cause errors, so that problem remained.

To eliminate the wire-like or metallic nanotubes, the Stanford team switched off all the good CNTs. Then they pumped the semiconductor circuit full of electricity.
All of that electricity concentrated in the metallic nanotubes, which grew so hot that they burned up and literally vaporised into tiny puffs of carbon dioxide. This sophisticated technique eliminated the metallic CNTs in the circuit.
The Stanford researchers created a powerful algorithm that maps out a circuit layout that is guaranteed to work no matter whether or where CNTs might be askew.
"This 'imperfections-immune design' (technique) makes this discovery truly exemplary," said Sankar Basu, a programme director at the National Science Foundation.

Researchers used this imperfection-immune design to assemble a basic computer with 178 transistors, a limit imposed by the fact that they used the university's chip-making facilities rather than an industrial fabrication process.
Their CNT computer performed tasks such as counting and number sorting. It runs a basic operating system that allows it to swap between these processes.
The study was published in the journal Nature.