Washington State University researchers used light to write a highly conducting electric path in a crystal. This opens up the possibility of transparent, three-dimensional electronics that, like an Etch-A-Sketch, can be erased and reconfigured. On the left, a photograph of a sample with four metal contacts. On the right, an illustration of a laser drawing a conductive path between two contacts.
Credit: Washington State University
Transparent, 3D electronics can be configured and erased like an Etch A Sketch. It serves as a proof of concept for a phenomenon that WSU researchers first discovered by accident 4 years ago. At the time, a doctoral student found a 400-fold increase in the electrical conductivity of a crystal simply by leaving it exposed to light. Matt McCluskey, a WSU professor of physics and materials science, has now used a laser to etch a line in the crystal. With electrical contacts at each end of the line, it carried a current.
“It opens up a new type of electronics where you can 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 actually is invisible electronics.”
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 photoconductivity,” also occurs at room temperature, an improvement over materials that require cooling with liquid nitrogen. “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,” said McCluskey. “It may not retain 100% of its conductivity, but it’s pretty big.”
Moreover, the circuit can be by erased by heating it on a hot plate and recast with an optical pen. “It’s an Etch A Sketch,” said McCluskey. “We’ve done it a few cycles. Another engineering challenge would be to do that thousands of times.”
https://news.wsu.edu/2017/07/27/wsu-physicists-write-light-turn-crystal-electrical-circuit/
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