The development of artificial electronic skins, composed of flexible sensors, requires the use of thin, light, resistant and flexible materials. The most recent manufacturing techniques in microelectronics now make it possible to meet these requirements. A team of MIT researchers has designed wireless and battery-free gallium nitride sensors capable of analyzing heartbeats, sweat and UV exposure.
According to the researchers, the prospects are great and this work is only the beginning of the adventure. In addition to being able to detect sodium, these new type sensors will one day be able to detect different types of vital biomarkers such as glucose or cortisol levels.
The disadvantages of current wearable sensors
In the field of e-health, portable sensors are on the rise. Among other things, they make it possible to measure the respiratory or heart rate, the temperature, the level of sweating, etc.
These wireless devices typically communicate via Bluetooth via battery-powered chips, which makes them bulky. Studies concerning the miniaturization of these sensors are multiplying and the most recent technologies now make it possible to design ultrathin and autonomous sensors.
Grow and Peel Ultrathin Semiconductor Films Using Remote Epitaxy
Some time ago, the team of Jeehwan Kim (the corresponding author of this study) developed a technique called remote epitaxy. This emerging technology¹ makes it possible to produce autonomous monocrystalline structures and thin films, that is to say without support.
Using this technique, researchers are notably able to produce high-quality ultrathin semiconductors from graphene-coated wafers. This allowed them to study different types of multifunctional and flexible electronic films.
Gallium nitride sensors
Gallium nitride (GaN), when it is pure and flawless, is an exceptional piezoelectric material, because it is very sensitive. GaN is capable of vibrating in response to an electrical impulse as well as producing an electrical signal following mechanical stress. MIT researchers have therefore exploited the properties of this material for both detection and wireless communication.
Furthermore, in order to improve the quality of the electrical signals, the samples were also covered with a layer of conductive gold. The whole thus forms an ultrathin sensor barely 250 nm thick (1/100th of a hair!).
The other advantage of these sensors is that they are not energy-intensive. They can thus be used directly on the body, for example in a bandage.
In a press release, Yeongin Kim, the study’s first author and former MIT postdoc, adds: “If there’s a change in the pulse, or chemicals in the sweat, or even ultraviolet exposure of the skin, all of that activity can change the pattern of surface acoustic waves on the gallium nitride film. »
By combining the device with a very fine membrane capable of detecting ions, the researchers were able to detect and transmit variations in the sodium level in the perspiration of a volunteer.
This supposes that by using other types of membranes, it would be possible to detect different types of biomarkers, in particular glucose or cortisol.
Image from Front page, credit: MIT
 To learn more about this new technique, you can also consult this other article published in Nature.