Stanford engineers have built a basic computer using carbon nanotubes (CNTs), a semiconductor material that has the potential to launch a new generation of electronic devices that run faster, while using less energy, than those made from silicon chips.
This unprecedented feat culminates years of efforts by scientists around the world to harness this promising but quirky material.
The research is reported in an article on the cover of the journal Nature.
About 15 years ago, CNTs were fashioned into transistors, the on-off switches at the heart of digital electronic systems; however, inherent imperfections in CNTs have stood in the way of outing this promising material to practical use.
Firstly, CNTs do not necessarily grow in neat parallel lines, as chipmakers would like. 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.
Secondly, depending on how the CNTs grow, a fraction of these carbon nanotubes can end up behaving like metallic wires that always conduct electricity, instead of acting like semiconductors that can be switched off.
The Stanford engineers found a way to deal with misaligned and/or metallic CNTs without having to search for them. They call their two-pronged approach an “imperfection-immune design”.
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 vapourised into tiny puffs of carbon dioxide. This sophisticated technique eliminated the metallic CNTs in the circuit.
Bypassing the misaligned nanotubes required even greater subtlety. The engineers sorted this problem out by creating a powerful algorithm that maps out a circuit layout that is guaranteed to work no matter whether or where CNTs might be askew.
The Stanford team 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. In a demonstration of its potential, the researchers also showed that the CNT computer could run MIPS, a commercial instruction set developed in the early 1980s by then Stanford engineering professor and now university President John Hennessy.
The new Stanford approach could very well lead to the mass production of carbon nanotube semiconductors and points to a new generation of electronic devices beyond silicon.
– Tom Abate | Stanford University
Source: Stanford University