Temperature-Switching Flexible Strain Sensors Based on Vanadium Dioxide for Intelligent Packaging Applications.

Flexible sensors are promising for intelligent packaging and artificial intelligence, but the required multistimulus response is still a challenge in external environments. A candidate material for such multistimulus response is VO 2 due to its unique semiconducting properties. Herein, W-doped VO 2 (M) with a tunable phase transition temperature was prepared by the hydrothermal method, and then, VO 2 (M)-based flexible sensors were fabricated employing a direct-write strategy, where conductive inks with VO 2 (M) powders were patterned onto various substrates. These sensors achieve dual responses to temperature and strain and exhibit high stability (over 2000 stretch-release cycles) to accurately monitor various statuses (opening and closing, temperature changes, etc.) of intelligent packaging. The spatial pressure distribution of different objects was discerned by the prepared VO 2 (M)/poly(dimethylsiloxane) (PDMS) sponge flexible pressure sensor arrays, and the information was successfully edited using the Morse code. The sensing signals from the intelligent packaging were collected and remotely transmitted to intelligent terminals via a wireless local-area network to achieve real-time monitoring of the packaged contents. Therefore, in this work, we not only designed new flexible sensors with multiple stimulus responses but also demonstrated the potential applications of W-doped VO 2 (M)-based flexible sensors in intelligent packaging.