Recrystallization-Induced Laser Lift-Off Strategy for Flexible Thermal Sensors with Near-Limit Sensitivity

Flexible thermal sensors have attracted immense interest as an alternative to conventional rigid sensors in personal healthcare monitoring, biomedical applications, and human-machine interaction. However, most metal-based flexible thermal sensors exhibit low sensitivity, primarily resulting from electron scattering due to manufacturing defects. The heat-intolerant polymer substrate hinders the pathway to improve the sensitivity of metal thin films through high-temperature annealing. Here, a recrystallization-induced laser lift-off strategy is proposed to overcome the contradiction between the flexible substrate and high-temperature annealing. Systematically theoretical and experimental studies reveal the mechanism of thermal-induced recrystallization in increasing the temperature coefficient of resistance (TCR) and the separation of sensors from rigid substrates. Valuable insights are acquired in the modulation of interface adhesion by altering the surface roughness of nickel. A critical temperature is provided to guide the detachment of the sensor. The fabricated thin-film flexible thermal sensor achieves a TCR of 6.2 parts per thousand degrees C-1, approaching the TCR limit of bulk material. This strategy opens a new general route for fabricating high-temperature annealed sensors on flexible substrates. A high-temperature annealing process is necessary for mitigating manufacturing defects in metal-based flexible thermal sensors. However, this poses a challenge for flexible polymer substrates. To overcome this conflict, a recrystallization-induced laser lift-off strategy is proposed. This approach aims to reduce defects in the metal film and create conditions for peeling, resulting in a flexible and highly sensitive thermal sensor.image