Sub‐Zero Temperature Sensor Based on Laser‐Written Carbon

Abstract Sub‐zero temperature sensors (SZTSs) have potential applications in safely storing COVID‐19 vaccines. Herein, an SZTS based on laser‐induced carbonization (LIC) achieved by a nanosecond infrared laser with a wavelength of 1064 nm is reported. Direct laser writing is adopted for laser‐induced carbon in Kapton polyimide sheets with a thickness of 125 µm. The sensor exhibits a good linear change in resistance to sub‐zero temperatures ranging from 0 to −150 °C, where the coefficient of determination adjusted R‐square (R 2 ) value is 0.99238, which indicates a good linear fit. The sensor exhibits a stable static response at all temperatures over time. The dynamic responses by controlling the liquid nitrogen gas and placing an ice cube on the sensor are also measured to validate the sensor. Notably, the electrical performance of the sensor remains stable even after 15 h. The sensor response of the LIC sample validates the 3D variable range‐hopping charge transport mechanism, governed by the Mott equation with a good linear fit, which is mainly owing to disorder in its structure. LIC‐based SZTSs can enable sensors that are ultra‐fast to fabricate, roll‐to‐roll processable, economical, and more significantly, can be interfaced with flexible printed circuit boards without any additional interfacing.