Page last updated at 10:14 GMT, Thursday, 1 May 2008 11:14 UK

Electronics' 'missing link' found

Hewlett-Packard's Stan Williams helped develop 'memristors'

Details of an entirely new kind of electronic device, which could make chips smaller and far more efficient, have been outlined by scientists.

The new components, described by scientists at Hewlett-Packard, are known as "memristors".

The devices were proposed 40 years ago but have only recently been fabricated, the team wrote in the journal Nature.

They have already been used to build novel transistors - tiny switches that are the building blocks of all chips.

"Now we have this type of device we have a broader palette with which to paint our circuits," Professor Stan Williams, one of the team, told the BBC last year.

Total recall

Memristors were first proposed in 1971 by Professor Leon Chua, a scientist at the University of California, Berkeley.

They are the "fourth" basic building block of circuits, after capacitors, resistors and inductors.


"I never thought I'd live long enough to see this happen," Professor Chua told the Associated Press.

"I'm thrilled because it's almost like vindication. Something I did is not just in my imagination, it's fundamental."

The memristors are so called because they have the ability to "remember" the amount of charge that has flowed through them after the power has been switched off.

This could allow researchers to build new kinds of computer memory that would would not require powering up.

Today, most PCs use dynamic random access memory (DRAM) which loses data when the power is turned off.

But a computer built with memristors could allow PCs that start up instantly, laptops that retain sessions after the battery dies, or mobile phones that can last for weeks without needing a charge.

"If you turn on your computer it will come up instantly where it was when you turned it off," Professor Williams told Reuters.

"That is a very interesting potential application, and one that is very realistic."

'Industry anathema'

Professor Williams and his team have already shown that by putting two memristors together - a configuration called a crossbar latch - it could do the job of a transistor.

Cross-bar latch
The team has built hybrid circuits using memristors and transistors

"A crossbar latch has the type of functionality you want from a transistor but it's working with very different physics," he explained.

Intriguingly, these devices can also be made much smaller than a conventional transistor.

"And as they get smaller they get better," he said.

As a result, the new devices could play a key part in the future of the electronics industry, as it relentlessly pursues Moore's Law.

This industry axiom, first stated by Gordon Moore, co-founder of chip-maker Intel, states that the number of transistors it is possible to squeeze in to a chip for a fixed cost doubles every two years.

However, according to some, it may be some time before the device is widely used.

"Even to consider an alternative to the transistor is anathema to many device engineers, and the memristor concept will have a steep slope to climb towards acceptance," wrote Drs James Tour and Tao Heare of Rice University, Houston, in an accompanying article in Nature.

They said that some in the electronics industry would only accept the use of memristors "after the demonstration of a well-functioning, large-scale array of these densely packed devices".

"When that happens, the race towards smaller devices will proceed at full steam."


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