Optical Innovation Could Vastly Improve Digital Imaging, Smoke Detection
The silicon phototransistor, which could help to enhance images captured in a low-light setting, depends upon electronic light sensors and mimics the behavior of the eyes of mammals.
MADISON, Wisc. – Electrical engineers at the University of Wisconsin-Madison said they have created the fastest, most responsive flexible silicon phototransistor ever made.
The phototransistor could improve the performance of myriad products – ranging from digital cameras, night-vision goggles and smoke detectors to surveillance systems and satellites – that rely on electronic light sensors, according to the engineers. Integrated into a digital camera lens, for example, it could reduce bulkiness and boost both the acquisition speed and quality of video or still photos.
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Developed by UW-Madison collaborators Zhenqiang “Jack” Ma, professor of electrical and computer engineering, and research scientist Jung-Hun Seo, the high-performance phototransistor far and away exceeds all previous flexible phototransistor parameters, including sensitivity and response time, according to the university.
Saying it was inspired by mammalian eyes, the researchers published details of the phototransistor in the journal Advanced Optical Materials.
Like human eyes, phototransistors essentially sense and collect light, then convert that light into an electrical charge proportional to its intensity and wavelength. In the case of human eyes, the electrical impulses transmit the image to the brain. In a digital camera, that electrical charge becomes the long string of 1s and 0s that create the digital image.
While many phototransistors are fabricated on rigid surfaces, and therefore are flat, Ma and Seo’s are flexible, meaning they more easily mimic the behavior of mammalian eyes.
“We actually can make the curve any shape we like to fit the optical system,” Ma says. “Currently, there’s no easy way to do that.”
One important aspect of the success of the new phototransistors is the researchers’ innovative “flip-transfer” fabrication method, in which their final step is to invert the finished phototransistor onto a plastic substrate. At that point, a reflective metal layer is on the bottom.
“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,” Ma says.
The researchers are patenting the technology through the Wisconsin Alumni Research Foundation.
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