06-08-2020 | | By Robin Mitchell
Recently, the Indian Institute of Technology Bombay (IIT-B), has developed an ultrathin optical sensor that can both detect light and generate power. What makes this sensor design unique, and how does it help the wearable electronics field?
Wearable electronics are devices that can be worn on the human body and provide useful functions, including task management, health monitoring, and tracking. While any device that is strapped to the body can be labelled as a wearable device, a truly wearable device should not only be comfortable to wear, it should almost act as an accessory. Thus, large beige boxes with heavy batteries strapped to the forearm cannot classify as wearable electronics. Devices such as smartwatches are far more useable, but even then these devices do not move organically with the body like material does.
The reason for wearable electronics still being a very niche market comes down to technological limitations. Most modern electronics are based on solid materials (such as semiconductors), which cannot flex. This means that some portion of a wearable device has to be based on a ridged piece of hardware and thus cannot flex. While some flexible components do exist (including PCBs), scientists are still yet to design flexible semiconductors that can be worn unknowingly to the user.
The ability to create flexible sensors is the first step for wearable electronics; flexible sensors allow for the creation of intelligent clothes that can wirelessly connect to a smartwatch or smartphone. From there, creating flexible sensors that are comfortable to wear helps with the commercialisation, which in turn provides more funds for the development of truly flexible devices.
To continue with the development of flexible electronics, the Indian Institute of Technology-Bombay (IIT-B), has released a paper on an ultrathin optical sensor that they have designed. According to the team of researchers, the sensor is useable in a wide range of different applications ranging from bioimaging, wearable electronics, environmental monitoring, and defence.
The optical sensor developed by the researchers utilises the wonder material, graphene, which has excellent optical characteristics. The ability for graphene to flex, while also remaining strong, makes the optical sensor ideal for use in flexible applications. For the sensor to work, multiple rounds of theoretical calculations were needed to be done to provide a strong foundation for the design. From there, different graphene layers were layered on top of each other, which produces a heterojunction. A heterojunction is the interference caused when two layers of dissimilar semiconductor are in contact with each other. A classic example of a heterojunction semiconductor device is the Bi-Polar Junction Transistor (BJT). Another feature expressed by the sensor is its ability to interact with a wide range of light from infra-red to visible (something that neither graphene layer can accomplish themselves). The creation of the sensor was done at ITT-Bs’ Nanofabrication Facility while the Tata Institute of Fundamental Research verified the results of the experiment.
While this device is only a prototype, it demonstrates the role that graphene could play in future devices. Flexible optical sensors could find themselves woven into material or devices which could provide information on the local environment, or provide a Li-Fi data link. Graphene-based solar cells could also become important in energy harvesting applications that can be easily wrapped around a design while adding very little weight. Optical sensors are also useable in health applications; visible light sensors are useful in apps that record heart rate non-invasively.