Instant-On Computing

Chips based on magnetic nanoparticles could lead to low-power, programmable logic.

As transistors have been made smaller and packed more densely onto computer chips, chips have consumed more and more power, quickly draining batteries and threatening to make laptops unbearably hot. This has many looking ahead to a day when something other than a transistor might serve as the workhorse of the computer processor.

One candidate for such an alternative technology recently took another step toward reality. As reported last week in the journal Science, researchers at Notre Dame have combined magnetic nanoparticles into a logic gate that theoretically could be used to perform all the operations of today’s computers. Instead of electricity, as in transistors, the technology uses the particles’ magnetic fields for processing information, leading the researchers to estimate that a computer based on this technology could run on a thousand times less power.

It’s experimental evidence for a theoretical approach that “could very well be the most efficient way of computing,” says Stan Williams, director of quantum science research at Hewlett-Packard, who calls the Notre Dame research “first rate.” While it’s unlikely to appear commercially in computers within the next decade, he says, “what it has done is inject a note of optimism that there are physical processes that can be used for computing that can be very, very low power consumption.”

Furthermore, since the process does not require power to maintain its settings, it could be the basis of instant-on computing, as well as a way to survive power outages, says Williams. “Somebody can pull the plug on you, and you can plug it in maybe five years later and the thing’s going to take up exactly where it left off and keep on going.”

At the heart of the new technology are magnetic nanoparticles that “flip” in response to the orientation of similar nearby particles – as refrigerator magnets sometimes flip over if they’re brought close together. In a row of such particles, flipping the first particle can cause the rest of the magnets to flip, similar to a row of dominoes falling. This, in effect, transmits the information about the first magnet’s position to the end of the row.

The Notre Dame researchers took this idea a step further, by surrounding one nanomagnet with four others. Three of them act as “inputs” and determine the position of the central magnet. This configuration, in turn, determines the position of the “output” magnet. One of the inputs can then be used as a master control, establishing what sort of logic the magnets carry out. For instance, if two inputs are in an “up” position, the output is a magnet in the “down” position. This programmable logic gate can be used to perform all the operations a computer might need to do.

Gary Bernstein, electrical engineering professor at Notre Dame and one of the researchers on the project, says challenges remain before the particles can be used for large-scale computing. “We need to get a little bit better handle on the process, so the magnets are more uniform,” he says. “Also we need to have a good input and output structure” for feeding information into multiple logic gates and retrieving it after the logic is performed.

The first applications may not completely replace transistors, but instead augment them – Bernstein believes the particles can be layered on top of existing computer chip architectures and incorporated into current manufacturing processes.

For now, though, having a working device is a significant step forward. “You can always have a design or theory, but until you’ve actually committed and built it, there’s a thousand types of ‘gotchas,’” HP’s Williams says. “It’s a very clever idea, and the fact that they built it gives it that much extra bit of reality.”

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