Phototransistors are rather important part of modern electronics. They are used in such commonly used products as compact disc players, smoke detectors, remote control devices and many more. They are even more important in scientific applications and equipment, such as photoconductors, charge-coupled devices, and photomultiplier tubes. Now electrical engineers at the University of Wisconsin-Madison have created a new kind of phototransistor and it is the fastest, most responsive flexible silicon phototransistor ever made.
Scientists say that this innovation may improve the performance of myriad products, such as digital cameras, night-vision goggles, smoke detectors, surveillance systems, satellites and other devices that rely on electronic light sensors. In fact, soon we all may see the benefits of this new technology, since these flexible phototransistors, integrated into a digital camera lens, should reduce bulkiness and boost both the acquisition speed and quality of video or still photos. These impressively wide possibilities for application are possible because of incredible properties of this device – new flexible phototransistor exceeds all previous flexible phototransistor parameters, including sensitivity and response time by a large margin.
Scientists say that this achievement was inspired by mammals’ eyes. Similarly to a human eye, these phototransistors sense and collect light. Then they convert this light into an electrical charge proportional to its intensity and wavelength. It is very similar to human eyes. When we see something, our eyes sense and collect light, which is then converted into electric impulses that go to our brain via nerves. Of course, electronic devices work differently – phototransistors in digital cameras sense light, which is then converted into a long line of 1s and 0s, which is used to form the image. However, our eyes are not flat, unlike most of contemporary phototransistors, which are made on rigid surfaces. The new phototransistors are flexible, which allows them to mimic eyes of mammals more accurately.
Engineers are rather proud of their achievement. They say that currently it is impossible to achieve desired curves in phototransistors, but the one developed at the University of Wisconsin-Madison can be made in any curve to fit any optical system. One of the most important technologies behind this achievement is innovative “flip-transfer” fabrication method. The final step in this method is inverting the finished phototransistor onto a plastic substrate. In this stage a reflective metal layer ends up being on the bottom. In this structure, coming light is not blocked by any metal layers or other materials. This means that this flexible phototransistor features much more efficient light absorption. Light is absorbed directly into an ultrathin silicon layer.
Scientists placed electrodes under this ultrathin silicon nanomembrane layer. This resulted in the metal layer and electrodes acting as reflectors, which improved light absorption. This means that an external amplifier is not needed. Scientists say that there is an integrated capability to sense weak light, which is beneficial for a variety of applications.
Professor Zhenqiang “Jack” Ma, one of the developers of this project, explained: “This demonstration shows great potential in high-performance and flexible photodetection systems. It shows the capabilities of high-sensitivity photodetection and stable performance under bending conditions, which have never been achieved at the same time”.
This is a great example, showing how rapidly electronics are developing these days. Even such small and invisible parts are getting more and more advanced and influence entire industry of electronic devices. In fact, since flexible phototransistor are used in cameras, it is likely that very soon we will soon see the results of this achievement in shape of better quality photos and videos.