Software can transform a computer from a word processor to a number cruncher to a video telephone. But the underlying hardware is unchanged. Now, a type of transistor that can be switched with magnetism instead of electricity could make circuitry malleable too, leading to more efficient and reliable gadgets, from smart phones to satellites.

Transistors, the simple switches at the heart of all modern electronics, generally use a tiny voltage to toggle between ‘on’ and ‘off’. The voltage approach is highly reliable and easy to miniaturize, but has its disadvantages. First, keeping the voltage on requires power, which drives up the energy consumption of the microchip. Second, transistors must be hard-wired into the chips and can’t be reconfigured, which means computers need dedicated circuitry for all their functions.

A research group based at the Korea Institute of Science and Technology (KIST) in Seoul, South Korea, has developed a circuit that may get around these problems. The device, described in a paper published on Nature’s website on 30 January, uses magnetism to control the flow of electrons across a minuscule bridge of the semiconducting material indium antimonide (S. Joo et al. Nature http://dx.doi.org/10.1038/nature11817; 2013). It is “a new and interesting twist on how to implement a logic gate”, says Gian Salis, a physicist at IBM’s Zurich Research Laboratory in Switzerland.

The bridge has two layers: a lower deck with an excess of positively charged holes and an upper deck filled predominantly with negatively charged electrons. Thanks to the unusual electronic properties of the indium antimonide, the researchers can control the flow of electrons across the bridge using a perpendicular magnetic field. When they set the field in one direction, electrons are steered away from the positive bottom deck and flow freely. When the magnetic field is flipped, the electrons crash into the lower deck and recombine with the holes — effectively turning the switch off (see ‘Magnetic lock’).

The ability of a magnetic logic gate to hold the switch on or off without a voltage “could lead to great reduction of energy consumption”, says study co-author Jin Dong Song, a physicist at KIST. Even more impressively, the magnetic switches “can be handled like software”, he says, by simply flipping the field to enable or disable a circuit. Thus a mobile phone could, for example, reprogram a bit of its microcircuitry to process video while its user watched a clip on YouTube, then switch the chip back to signal processing to take a phone call. This could greatly reduce the volume of circuitry needed inside the phone.

Such reconfigurable logic could be invaluable in satellites, adds Mark Johnson of the Naval Research Laboratory in Washington DC, a co-author of the paper. If part of a chip failed in orbit, another sector could simply be reprogramed to take over. “You’ve healed the circuit and you’ve done it from Earth,” he says.

To really catch on, however, the magnetic logic would have to be integrated with existing silicon-based technologies. That may not be easy. For one thing, indium antimonide, the semiconductor crucial to the circuits, doesn’t lend itself well to manufacturing processes used to make modern electronics, according to Junichi Murota, a researcher working with nanoelectronics at Tohoku University in Japan. But Johnson says that it may eventually be possible to build similar bridges with silicon.

Integrating the miniature magnets needed to control the devices into a normal chip wouldn’t be easy either. Companies should be able to solve these challenges, but only if they decide the devices are worthwhile, says Salis. At the moment, he adds, it is not clear whether the devices will perform well at the sizes needed for a practical chip — much smaller than the micrometer dimensions of the prototypes.

5 Comments

1. 1. jtdwyer 06:16 PM 1/30/13

   This is interesting fundamental research, but the articles says:
   "The voltage approach is highly reliable and easy to miniaturize, but has its disadvantages. First, keeping the voltage on requires power, which drives up the energy consumption of the microchip. Second, transistors must be hard-wired into the chips and can’t be reconfigured, which means computers need dedicated circuitry for all their functions."
   
   1) Can the magnetic switch be continuously miniaturized as the voltage switch has been over these many decades?
   
   2) Power requirements are a fundamental issue for voltage based switching, but they are also reduced with miniaturization.
   
   3) Is there any real requirement or demand for dynamic hardware reconfiguration, or is this simply a capability of magnetic switches in search of a requirement, being portrayed here as a disadvantage for electronic devices? To the extent that there is any requirement for reconfiguration, hardware circuitry supports using reduced instruction sets that can emulate varying instruction sets, allowing a single chip architecture to perform various dedicated functions. 'Self-healing' capabilities similar to those described could be provided in electronic circuits by having unused circuit capacity that could be dynamically microprogrammed to recover some failed component for some hypercritical applications (processors on board satellites subject to cosmic radiation, for example), for most applications processor reliability is more than adequate. How many PCs suffer from processor failure?
   
   Again, interesting research, but at this point mostly a solution in search of a problem...

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2. 2. Autaut in reply to jtdwyer 07:08 PM 1/30/13

   Mostly true,
   
   However i might note, there are actually reconfigurable circuits available. they are called FPGA and come with two characteristics, that make runtime-rearranging unattractive:
   First, it takes a considerable amount of data to store the layout, which means "reprogramming" it takes time on the order of millis. This is days in processor time.
   On the other hand, they require a generic logic layout that leads to poor logic densities compared to ASICs (application specific IC).
   They are not widely used, because mass-produced ASICs are more powerfull and cost less.
   
   By the way, there is a flaw in the reasoning about power consumption:
   Today's ICs use MOSFET transistors which have an isolated gate. This means, holding the voltage takes only a very small amount of current. As we know, power is the product of both.
   Infact, very high current is needed to change the state of the transistors, even if only for a short time.
   This switching current accounts for the vast amount of power dissipation in all high frequency applications.
   (yes, that's the main reason why stepping down the clock on an idle cpu saves battery)
   
   This principle would also apply to such magnetic gates, as power is required to run through the magnetic hysteresis.

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3. 3. jtdwyer in reply to Autaut 07:33 PM 1/30/13

   Thanks for clarifying my potshots - I figured I'd hit something, with such a large target!

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4. 4. priddseren 10:00 PM 1/30/13

   While there could be some interesting if limited application of this technology, perhaps combined with the concept of medical nanobots that could be reprogrammed magnetically from outside the body it still suffers from the same basic problem all advances in computers have. The use of binary states for processing information. This is around 1940 tech and all that has occurred since then is making systems do this faster but still it is the same thing. The human brain doesn't use binary math and is able to achieve far more raw computing power than super computers, running on the energy of a carrot.
   The real advance in computers will be when someone invents a CPU that uses something more advanced than binary math.
   
   This problem occurs elsewhere. The 4 stroke internal combustion engine is a good example. Yeah, we have faster, better, more efficient engines today but in the end all we have done is taken an invention from the late 19th century and we just keep improving the devices doing it but we have not really come up with something more advanced. Or if there is something better, it has not displaced the over century old 4 stroke engine.
   
   These magnetic circuits are the same thing done a different way and not all that innovative from the perspective of computer processing. More of an innovation in electrical engineering.

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5. 5. komorkowy 11:38 AM 2/7/13

   Hello First of all, magnetic keeping the voltage on requires power on this website is explanation how does it work http://www.electrogsm.pl which drives up the energy consumption of the microchip. Second, transistors must be hard-wired into the chips and can’t be reconfigured

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