Inspired by mammals' eyes, University of Wisconsin-Madison electrical engineers have created the fastest, most responsive flexible silicon phototransistor ever made. The innovative 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. 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. Developed by UW-Madison collaborators Zhenqiang "Jack" Ma, Ph.D., Professor of Electrical and Computer Engineering, and Research Scientist Jung-Hun Seo, Ph.D., the high-performance phototransistor far and away exceeds all previous flexible phototransistor parameters, including sensitivity and response time. The researchers published details of their advance online on October 26, 2015 in the journal Advanced Optical Materials. The article is titled “Flexible Phototransistors Based on Single-Crystalline Silicon Nanomembranes.” 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 our eyes, the electrical impulses transmit the image to the brain. In a digital camera, that electrical charge becomes the long string of 1’s and 0’s that create the digital image. While many phototransistors are fabricated on rigid surfaces, and therefore are flat, the phototransistors created by Dr. Ma and Dr. Seo 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," Dr. Ma says. "Currently, there's no easy way to do that."
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