Posted: May 24, 2018 |
Silicon breakthrough could make key microwave technology much cheaper and better
(Nanowerk News) Researchers using powerful supercomputers have found a way to generate microwaves with inexpensive silicon, a breakthrough that could dramatically cut costs and improve devices such as sensors in self-driving vehicles (Scientific Reports, "Gunn-Hilsum Effect in Mechanically Strained Silicon Nanowires: Tunable Negative Differential Resistance").
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"Until now, this was considered impossible," said C.R. Selvakumar, an engineering professor at the University of Waterloo who proposed the concept several years ago.
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High-frequency microwaves carry signals in a wide range of devices, including the radar units police use to catch speeders and collision-avoidance systems in cars.
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The microwaves are typically generated by devices called Gunn diodes, which take advantage of the unique properties of expensive and toxic semiconductor materials such as gallium arsenide.
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When voltage is applied to gallium arsenide and then increased, the electrical current running through it also increases - but only to a certain point. Beyond that point, the current decreases, an oddity known as the Gunn effect that results in the emission of microwaves.
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Lead researcher Daryoush Shiri, a former Waterloo doctoral student who now works at Chalmers University of Technology in Sweden, used computational nanotechnology to show that the same effect could be achieved with silicon.
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The second-most abundant substance on earth, silicon would be far easier to work with for manufacturing and costs about one-twentieth as much as gallium arsenide.
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The new technology involves silicon nanowires so tiny it would take 100,000 of them bundled together to equal the thickness of a human hair.
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Complex computer models showed that if silicon nanowires were stretched as voltage was applied to them, the Gunn effect, and therefore the emission of microwaves, could be induced.
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"With the advent of new nano-fabrication methods, it is now easy to shape bulk silicon into nanowire forms and use it for this purpose," said Shiri.
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Selvakumar said the theoretical work is the first step in a development process that could lead to much cheaper, more flexible devices for the generation of microwaves.
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The stretching mechanism could also act as a switch to turn the effect on and off, or vary the frequency of microwaves for a host of new applications that haven't even been imagined yet.
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"This is only the beginning," said Selvakumar, a professor of electrical and computer engineering. "Now we will see where it goes, how it will ramify."
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