26-08-2021 | | By Sam Brown
Recently, researchers from NTU Singapore have created a flexible UV sensor that can be manufactured using standard semiconductor foundries. What challenges does UV present, what did the researchers develop, and how will such developments help create wearable systems?
Ultraviolet light (UV) is light whose wavelength is between 100 nm to 400 nm, placing it between visible light and x-rays. UV is further split into sub-categories of decreasing wavelength from UVA to UVC, meaning that UVA is the least energetic UV light while UVC is the most energetic.
UV is particularly problematic to living organisms as it has enough energy to damage DNA on a molecular level. While this can be advantageous for destroying microbes and viruses, it also means that it can damage and destroy skin cells. Destroying skin cells is one thing, but damaging their DNA is far worse, leading to skin cancers. This is why wearing sunscreen is so vital during days that have a high UV index.
Trying to determine UV exposure is complex, and one method would be to use wearable devices. A small UV sensor could accumulate exposure results over the day to inform the wearer if they have been exposed for too long. However, most wearable devices are cumbersome, making them very impractical. Furthermore, conditions that see high levels of UV will most likely encourage less clothing, meaning that wearable devices become even less likely to be worn.
Recognising the need for flexible sensors, researchers from the Nanyang Technological University, Singapore, recently announced a flexible UV sensor development. The device is reported to be over 25 times more responsive than previous designs and over 330 times more sensitive. Furthermore, the sensor can be flexed and manipulated over 100 times while retaining sensitivity with a responsivity level of between 530 and 1340 A/W.
Constructing the sensor was achieved by layering free-standing single-crystal layers of GaN and AlGaN on an 8-inch wafer whose arrangement was altered using two different thin semiconductor layers. The researchers do not specifically mention which semiconductor materials were used, but the term “heterostructure membranes” is mentioned, which refers to a semiconductor whose property changes with depth.
Of all the industries that electronics has managed to integrate itself into, wearables are the one industry that electronics has genuinely struggled to enter. This is because electronics are inherently rigid and inflexible, making them impractical to integrate into clothing and other body-worn devices.
If electronics could be integrated into clothes and comfortable wearables, the applications for such devices go far beyond smart devices and social media; healthcare could be significantly improved. A wearable medical device that can continually monitor an individual could provide predictive analysis on their vitals to determine if the user is falling ill. Such a device could be combined with a flexible UV sensor to determine the cancer risk of being in the sun and warn the user if overexposed.
Developing such electronic systems will take time, but there are many promising results already in flexible electronics. In the coming decades, wearable electronics will start to see their introduction into wrist-worn devices that are comfortable to wear (unlike Smart Watches) and may eventually find their way into clothing.