Electrical engineers from the University of Wisconsin have developed a flexible silicon phototransistor, which to date is the fastest and most responsive ever created. The innovation has the potential to improve a range of products, from digital cameras to satellites, which depend on electronic light sensors.

Just like mammalian eyes, phototransistors collect light and then transform this into an electrical impulse. In mammals, this pulse is transported by the brain's nerves but in digital devices, the electrical charge becomes a binary code that software converts into a digital image.

Many phototransistors are flat because they are fabricated on rigid surface but the new phototransistor is flexible so it can easily mimic the behavior of the eyes of mammals.

The technology outperforms earlier flexible phototransistors when it comes to sensitivity and response times.  It can notably be integrated into digital cameras, where it could make possible the delivery of clearer and higher definition images even in low-light settings.

"Due to the good mechanical flexibility of Si NMs with the assistance of a polymer layer to enhance light absorption, the device exhibits stable responsivity," the researchers wrote in their study, which was published in the journal Advanced Optical Materials on Oct. 26.

"Overall, such flexible phototransistors with the capabilities of high sensitivity light detection and stable performance under the bending conditions offer great promises for high-performance flexible optical sensor applications, with easy integration for multifunctional applications."

The researchers said that the groundbreaking phototransistor has a built-in capability to sense weak light. Electrodes were attached under the silicon nanomembrane layer of the phototransistor. The metal layer and the electrodes individually serve as reflector and boost absorption of light sans the need for an external amplifier. 

The researchers said that unlike in other photodetectors, absorption of light in an ultrathin silicon layer is more efficient due to light not being blocked by any layer of material.

Researchers are optimistic about the possible outcome of the technology. The record-setting transistor, for instance, can pave way for more compact devices that are faster and marked by improved quality of videos and photos. The phototransistor may also be integrated into satellites, night-vision goggles, and medical imaging instruments.

"This demonstration shows great potential in high-performance and flexible photodetection systems," said study researcher Zhenqiang Ma, from University of Wisconsin-Madison. "It shows the capabilities of high-sensitivity photodetection and stable performance under bending conditions, which have never been achieved at the same time."

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