Transparent, Anti-Freezing Hydrogels for Ultrasensitive Temperature and Strain Sensor Based on A Thin-Film Structure

A thin film sandwich structure (TFSS) was designed to improve the wearing comfort, sensing performance, immunity to humidity, and miniaturization of the hydrogel sensor synchronously. The TFSS sensor was fabricated using the layer-by-layer spin-coating technology with a thickness of only $12.15\ \mu\mathrm{m}$ for the LiBr-percolated hydrogel layer. Benefiting from the ultrathin device structure, the low thermal capacity of LiBr solution, new capacitance measurement mode and ionic transport manner, the TFSS thermistor displays unprecedented sensitivity of 24.54%/°C, ultrafast response time (0.19 s), recovery time (0.08 s), high resolution (0.8 °C) and a broad detection range (−30∼96 °C). The sensitivity of our temperature sensor is one order of magnitude higher than those of state-of-the-art stretchable temperature sensors. In addition to temperature, the tensile strain can also be selectively detected with distinguishable signals, endowing the bimodal sensor with multifunctional sensing capability.