Physicists turn a crystal into an electrical circuit

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3D electronics

Washington State University physicists found a way to write an electrical circuit into a crystal, opening up the possibility of transparent, three-dimensional electronics, like an Etch A Sketch, can be erased and reconfigured.

The work serves as a proof of concept for a phenomenon that researchers first discovered by accident four years ago. At the time, a doctoral student found a 400-fold increase in the electrical conductivity of a crystal simply leaving it exposed to light.

Matt McCluskey, a WSU professor of physics and materials science, used a laser to etch a line in the crystal. With electrical contacts at each end of the line, it carried a current.

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It opens a new type of electronics where to define a circuit optically and then erase it and define a new one, said McCluskey. It’s exciting that it’s reconfigurable. It’s also transparent. There are certain applications where it would be neat to have a circuit that is on a window or something like that, where it invisible electronics.

persistent photo conductivity

Ordinarily, a crystal does not conduct electricity. But, when the crystal strontium titanate is heated under the right conductions, it is altered, so light will make it conductive. The phenomenon, called “persistent photo conductivity,” also occurs at room temperature, an improvement over materials that require cooling with liquid nitrogen.

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“We’re still trying to figure out exactly what happens,” said McCluskey. He surmises that heat forces strontium atoms to leave the material, creating light-sensitive defects responsible for the persistent photoconductivity.

McCluskey’s recent work increased the crystal’s conductivity 1,000-fold. The phenomenon can last up to a year. We look at samples that we exposed to light a year ago and they’re still conducting. It may not retain 100 percent of its conductivity, but it’s pretty big.

Moreover, the circuit can erase by heating it on a hot plate and recast with an optical pen. We’ve done it a few cycles. Another engineering challenge would be to do that thousands of times. This research particularly relevant to the challenge of Smart Systems and its theme of foundational and emergent materials.

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