Pillalamarri Srikrishnarka
Chennai: For accurate and fast thermal sensing, scientists have successfully fabricated a flexible temperature sensor.
Non-invasive wearable technologies have been gaining a lot of traction in the recent past. Technologies such as smart-watches can be further embedded with flexible sensors that enable users to capture multi-dimensional data.
Besides monitoring the heart rate, ECG, SPO2, and steps count, the temperature is one crucial parameter where a flexible, fast-responsive sensor can be used. Flexible temperature sensors, ultrathin conformal, and a fast-responsive nature have multiple applications in various fields.
Dr. Alwin Daus and their team recently fabricated a flexible thermal sensor based on molybdenum disulfide (MoS2) capable of responding in a few microseconds.
Firstly, MoS2 was grown using chemical vapor deposition (CVD) on a Si@SiO2 substrate. Later, gold electrodes were evaporated and deposited on this grown MoS2 for electric contacts. A thin layer of polyimide was spin-coated after curing; this enabled the transfer of the grown MoS2 with gold contacts onto the polyimide layer. This is a conformal polymer, and thickness can be altered based on the requirement. Alumina was finally deposited on the sensor as a capping agent.
“We found that the microscope light, used for probing the contact pads, led to some charge generation and trapping that persists even after the light was turned off.” To offset this, the authors performed all the experiments in the dark.
MoS2 is known to be highly reactive with air and moisture when heated, this leads to an increase in conductance. This issue was ingeniously solved by capping the sensor with alumina. “Al2O3 is an excellent barrier for gas diffusion and has commonly been used for passivation in flexible electronic devices because dense and high-quality films can be obtained at low temperatures that are compatible with flexible plastic substrates.”
The sensor is sensitive in the temperature range from 27 to 120 oC with a response time of 35 microseconds.
“All materials used here are biocompatible, and our temperature sensitivity estimations indicate a suitability for future biomedical applications such as skin or breast cancer detection and wound healing, but we note that other use cases may require sensitivity improvements,” concluded the authors.
These results have been published recently in ACS Nanoletters.