Faster and more flexible computers that utilise electron spin, as well as charge, appear feasible based on a novel design by a US research group.
Conventional microprocessors are rapidly approaching their physical limits, as researchers scramble to pack more and more computational power into smaller and smaller areas.
Spintronic circuitry, which utilises the quantum spin of electrons as well as their charge, promise a way around this impasse, but so far that promise has not been realised using conventional semiconductor materials.
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Now, researchers at the University of California, San Diego, in the US, have drawn up plans for a semiconductor-based spintronic device that performs the same logical operations as the transistors in a normal silicon chip. They have also shown how its spintronic logic gates could be integrated into large-scale integrated circuits.
鈥淭his is a first proposal on how to realise a real machine out of spin-based devices,鈥� says Hanan Dery, who led the project. 鈥淲e want to do this in your processor.鈥�
Spin accumulation
Dery and colleagues Parin Dalal, Lukasz Cywinski, and Lu Jeu Sham propose a device based on five microscopic bar-shaped magnetic contacts 鈥� two outer pairs flanking a single central one 鈥� along a strip of semiconducting material.
The magnetisation of the pair of bars at each end of the strip controls how many electrons with spin oriented in a particular direction can accumulate in the underlying semiconductor.
This 鈥渟pin accumulation鈥�, in turn, controls the output signal from the middle bar when its magnetic direction is reversed or when it is stimulated with an electrical signal. This signal represents the result of a particular logical computation.
The direction of magnetisation of the two outer bars represents a single bit of information, while the direction of magnetisation of the next two bars determines what logical operation will produce the signal from the central bar.
For example, the two end bars could be set to represent 1 and 0, and the two inner bars could check whether they are the same or different 鈥� and reflect the result in its output signal.
The group modelled the behaviour of the device in software, based on the known properties of its components. The simulations suggest that it could act as the primary logic gate of an information-processing circuit, and could be scaled down to compete with silicon-based technology.
Chameleon circuits
The researchers went on to show that such logic components could be linked together to make functioning integrated circuits. Unlike silicon-based processors, spintronic ones could also, in effect, be rewired at will 鈥� simply by changing the magnetization of the logic gates. 鈥淯sing spin you have a circuit that behaves like a chameleon,鈥� says Dery.
Some researchers in the field see this as a significant step forwards. 鈥淚 think it鈥檚 a very exciting, concrete idea,鈥� says Berend Jonker, a physicist at the US Naval Research Laboratory, in Washington, D.C.
鈥淭his is precisely what the field of semiconductor spintronics needs,鈥� Jonker adds, 鈥渟ome solid proposals for real-life devices and a competent analysis of their performance in the context of existing silicon devices.鈥�
Others, however, like Nitin Samarth at Pennsylvania State University in the US, add that the path from drawing board to working device may yet prove problematic. 鈥淭he implementation will be challenging,鈥� he says. 鈥淭he devil is always in the details.鈥�
Journal reference: Nature (p 573, vol 447)
