Real-time temperature detection using a flexible sensor can open up a variety of new possibilities. However, owing to the limited heat capacity of the detection materials and encapsulation problems, obtaining quick, sub-millisecond reaction times using a flexible sensor is still a significant challenge.
Study: Fast-Response Flexible Temperature Sensors with Atomically Thin Molybdenum Disulfide. Image Credit: Sambulov Yevgeniy/Shutterstock.com
A recent study published in the journal Nano Letters addresses this problem by creating a flexible sensor out of monolayer molybdenum disulfide (MoS2), capable of sensing temperature variation in a few microseconds, about 100 times faster than typically used thin-film metal detectors.
Real-time Thermal Detection using a Flexible Sensor
Temperature, the most basic physical variable reflecting the condition of the measured object and its surroundings, fluctuates with both time and location. Temperature control is critical in daily and industrial settings, and real-time temperature sensing has received increasing attention in recent years.
Many biomedical systems, pollution management, and safety-critical machine control systems need quick and reliable heat readings. Flexible sensor components are often required to be directly connected to human tissue or curved surfaces for consistent and accurate data readings in real-time thermal detection systems.
As a result, implementing next-generation temperature detectors on extremely thin, homogeneous, and flexible platforms is critical for enhanced interaction with biological materials and facile sensor implantation in biodegradable packaging or electrical components.
Flexible Temperature Sensors Based on 2D Materials
Flexible temperature sensors based on two-dimensional (2D) materials have recently shown significant promise in a variety of applications, including portable electronics, robotic systems, medical services, and prosthetics. Due to the non-toxicity and biocompatibility of many 2D materials, a flexible sensor based on these materials can be employed in implantable electronics for real-time thermal sensing.
Two-dimensional (2D) nanomaterials such as graphene and carbon nanotubes (CNTs) have recently emerged as promising candidates for flexible thermal detectors with exceptional responsiveness. However, two-dimensional (2D) semiconductors like molybdenum disulfide (MoS2), having virtually untapped potential for such applications, have not received much attention.
Molybdenum Disulfide for Fabrication of a Flexible Sensor
Previous research on molybdenum disulfide has shown it possesses significant potential as a novel sensing material. Molybdenum disulfide has great cytocompatibility and a high thermal coefficient of resistance (TCR), but its real-time sensing efficiency and array integration capabilities have yet to be investigated.
In this study, the researchers fabricated a flexible sensor for fast and accurate thermal detection from atomically thin molybdenum disulfide, using a recently developed direct transfer technique.
To realize this flexible sensor, chemical vapor deposition is used to create consistent single-layer molybdenum disulfide sheets. Gold contacts are deposited and the molybdenum disulfide coating is structured before the molybdenum disulfide films are transported to flexible platforms. The surface is then spin-coated with a 5-micron thick bendable polyimide (PI) substrate. This results in a molybdenum disulfide surface with exceptionally low surface roughness.
The researchers also built four-by-four panels of the as-fabricated molybdenum disulfide temperature detectors to illustrate the viability of this unique material for producing a low-cost flexible sensor for real-time temperature monitoring.
Important Findings of the Study
The researchers discovered that the as-fabricated flexible sensor had a thermal response time of 36 microseconds, many orders of magnitude faster than the conventionally used thin-film metal sensors. Thermal analyses suggest that the molybdenum disulfide contacts and encapsulation solely restrict the flexible sensor's reaction time.
The as-prepared flexible sensor exhibits a remarkable thermal coefficient of resistance, consistent operation during cycling, and long-term thermal measurement capabilities when capped with alumina.
The contact of the molybdenum disulfide surface with air and moisture, which normally takes several minutes to settle, can be ascribed to the ongoing rise in conductivity of the uncapped flexible sensor after heating. On the other hand, alumina capping is enough to passivate the molybdenum disulfide surface and stabilize the produced flexible sensor response.
In short, fast temperature detection is critical for real-time readout in large panels and, for example, detecting microsecond temperature surges in power electronic devices to avoid mechanical damage. Overall, the results of this work can lead to the development of widespread real-time temperature sensors using atomically thin semiconductors like molybdenum disulfide.
Daus, A., Jaikissoon, M., Khan, A. I., Kumar, A., Grady, R. W., Saraswat, K. C., & Pop, E. (2022). Fast-Response Flexible Temperature Sensors with Atomically Thin Molybdenum Disulfide. Nano Letters. Available at: https://pubs.acs.org/doi/10.1021/acs.nanolett.2c01344