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Computers that mimic brain function might be a step closer

07 April 2015

US researchers report an advance in electronics that could bring brain-like computing closer to reality - all thanks to a device called a 'memristor'.

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Both academic and industrial laboratories are working to develop computers that operate more like the human brain. Instead of operating like a conventional, digital system, these new devices could potentially function more like a network of neurons.

“Computers are very impressive in many ways, but they’re not equal to the mind,” says Mark Hersam, of Northwestern University’s McCormick School of Engineering. “Neurons can achieve very complicated computation with very low power consumption compared to a digital computer.”

A team of Northwestern researchers, including Hersam, has accomplished a new step forward in electronics that could bring brain-like computing closer to reality. The team’s work advances memory resistors, or 'memristors', which are resistors in a circuit that 'remember' how much current has flowed through them.

“Memristors could be used as a memory element in an integrated circuit or computer,” says Hersam. “Unlike other memories that exist today in modern electronics, memristors are stable and remember their state even if you lose power.”

Current computers use random access memory (RAM), which moves very quickly as a user works but does not retain unsaved data if power is lost. Flash drives, on the other hand, store information when they are not powered but work much slower.

Memristors could provide a memory that is the best of both worlds: fast and reliable. But there’s a problem: memristors are two-terminal electronic devices, which can only control one voltage channel. Hersam wanted to transform it into a three-terminal device, allowing it to be used in more complex electronic circuits and systems. 

Mark Hersam

Hersam and his team met this challenge by using single-layer molybdenum disulphide (MoS2), an atomically thin, two-dimensional nanomaterial semiconductor. Much like the way fibres are arranged in wood, atoms are arranged in a certain direction ('grains') within a material. The sheet of MoS2 that Hersam used has a well-defined grain boundary.

“Because the atoms are not in the same orientation, there are unsatisfied chemical bonds at that interface,” says Hersam. “These grain boundaries influence the flow of current, so they can serve as a means of tuning resistance.”

When a large electric field is applied, the grain boundary literally moves, causing a change in resistance. By using MoS2 with this grain boundary defect instead of the typical metal-oxide-metal memristor structure, the team presented a novel three-terminal memristive device that is widely tunable with a gate electrode. Hersam again:

“With a memristor that can be tuned with a third electrode, we have the possibility to realise a function you could not previously achieve. A three-terminal memristor has been proposed as a means of realising brain-like computing. We are now actively exploring this possibility in the laboratory.”

The research is described in the April 6 issue of Nature Nanotechnology.


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