Ultrathin Fiber-Mesh Polymer Thermistors

Flexible sensors enable on-skin and in-body health monitoring, which require flexible thermal protection circuits to prevent overheating and operate the devices safely. Here, ultrathin fiber-mesh polymer positive temperature coefficient (PTC) thermistors via electrospinning are developed. The fiber-type thermistors are composed of acrylate polymer and carbon nanofibers. The fibrous composite materials are coated with a parylene to form a core-sheath structure, which improves the repeatability of temperature characteristics. Approximately 5 µm thick fiber-type thermistors exhibit an increase in the resistance by three orders of magnitude within ≈2 °C and repeatable temperature characteristics for up to 400 cycles. The mesh structure enables the thermistor layer to be ultra-lightweight and transparent; the mesh-type thermistor operates with a fiber density of 16.5 µg cm^-2 , whose fiber layer has a transmittance of more than 90% in the 400-800 nm region. By fabricating the mesh thermistor on a 1.4 µm thick substrate, the thermistor operates without degradation when wrapped around a 280 µm radius needle. Furthermore, the gas-permeable property is demonstrated by fabricating the fibrous thermistor on a mesh substrate. The proposed ultrathin mesh polymer PTC thermistors form the basis for on-skin and implantable devices that are equipped with overheat prevention.