transistor-based logic gates in computer chips, according to a new study.
The research suggests that today’s transistors, which will approach their limits of miniaturisation sometime in the next couple of decades, could eventually be replaced by more shrinkable nanomagnet technology – allowing ever more powerful, faster processors to continue to be constructed.
Better still, the function of the magnetic logic gates can be changed after the hardware has been built, meaning that hardware could be “reprogrammed” – potentially making gadgets that use them far more versatile.
Logic gates are fundamental circuit components used to process information, which turn several inputs into one output, depending on the input signal combinations.
Until now, the only place magnetic devices have replaced electronic components is in an emerging class of chip called a Magnetic Random Access Memory. MRAMs keep frequently-used software or data stored permanently in magnetic cells, so there is no need to load it slowly from a disc. This makes boot-up times far faster.
But there has been no magnetic device that can “think” – or process information – in the way transistor-based logic gates do.
The beginnings of a magnetic version came five years ago when Russell Cowburn and colleagues at Imperial College London, UK, discovered that rows of nanomagnets could pass information along them.
Magnetic fields from each nanomagnet coupled with that of the next, so a north-south oriented magnet induced a south-north pole in the adjacent one, and so on. “We found information could be passed down the chain of nanomagnets,” Cowburn explains.
Now Alexandre Imre and colleagues in the nanoengineering department at the University of Notre Dame in Indiana, US, have taken Cowburn’s work even further.
“They have made a major step forward by showing that you can use nanomagnets to produce a universal logic gate, from which you can build any other logic circuit you like,” Cowburn says
NAND and NOR
Imre’s team have made a universal logic gate called a majority inverter. From this they can make any other type of logic gate needed for a circuit, including two critical logic gates known as NAND and NOR gates. All possible logic circuits can be made with these.
And because the gates are based on magnets they can be switched from one to another easily, allowing processors built from nanomagnets to be reprogrammed to do different jobs while they are in use, says the team.
Simulations show processing speeds of at least 100 megahertz should be possible using magnets 110 nanometres wide – with smaller ones expected to do much better. Consumer computer processors function at 2 or 3 gigahertz.
In Notre Dame’s tests, input signals were created using driver magnets placed near the gate’s input magnets. But a functioning nanomagnetic chip would use small currents flowing in a grid of nanowires to induce magnetic fields where they are needed.
But much work remains before such a technology becomes a reality. One of many the challenges will be to protect the delicate magnets from damaging heat and extraneous magnetic fields.
Cowburn, who is working with MRAM makers on developing the technology, suggests a common magnetic shielding material may have to be built into such chips. Called mu-metal, it is an alloy of nickel, iron, copper and molybdenum. “It’s effectively a Faraday Cage for magnetic devices,” he explains.
Journal reference: Science (vol 311, p 183)