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Groundbreaking silicon phototransistor developed by UW-Madison engineers

Electrical engineers just created the world’s fastest and most responsive phototransistor ever which can potentially improve the technology of a myriad of gadgets from digital cameras to satellites, depending on their light sensors. It’s because they act like our eyes do, turning light into an electrical pulse that, in the case of mammals, is sent to the brain, and in the case of digital cameras, transcribed into code and then turned into an image. Most of the existing phototransistors are made on rigid surfaces and therefore is flat – however the new version is bendable and very flexible meaning it can easily imitate the behavior of human or any other mammal’s eyes.

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The new discovery displays the capabilities of high-sensitivity photodetection and constant performance under twisting conditions, which have never been attained.

The highlight of the newly developed transistor is its size, which can be used to improve products like digital cameras, night vision instruments, surveillance systems, smoke detectors and satellites.

The researchers have published details of their advance in the journal Advanced Optical Materials. In a digital camera, that electrical charge becomes the long string of 1s and 0s that create the digital image. The small size of the transistor could reduce the bulkiness and boost up the acquisition speed and quality of the video or still photos.

“We actually can make the curve any shape we like to fit the optical system”, Massachusetts says.

The new advanced phototransistor’s flexibility and performance exceeds other types of phototransistors, and it is more like a pair of human eyes, according to the researchers. “Currently, there’s no easy way to do that”. They say they relied on a “flip-transfer” method, a totally new way of creating this product in which the finished piece is inverted into a plastic substrate, allowing light to be absorbed more efficiently and greatly.

“In this structure – unlike other photodetectors – light absorption in an ultrathin silicon layer can be much more efficient because light is not blocked by any metal layers or other materials”, Professor Massachusetts informed.

The tag-teaming bottom layer metal and electrodes negate the need for an external amplifier.

Citation: “Flexible Phototransistors Based on Single-Crystalline Silicon Nanomembranes”, Seo, J.-H., Zhang, K., Kim, M., Zhao, D., Yang, H., Zhou, W. and Massachusetts, Z.

“There’s a built-in capability to sense weak light”, Massachusetts says.

The technology will be patented though the Wisconsin Alumni Research Foundation (WARF).

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The new high-performance transistor has been developed by UW-Madison collaborators Zhenqiang “Jack” Massachusetts, professor of electrical and computer engineering researcher scientist Jung-Hun Seo.

High-Performance Flexible Si Phototransistors