Femtosecond laser-induced graphene for temperature and ultrasensitive flexible strain sensing

Flexible sensors with high sensitivity and stability are essential components of electronic skin, applicable to detecting human movement, monitoring physiological health, preventing diseases, and other domains. In this study, we utilized a straightforward and efficient femtosecond laser direct writing technique using phenolic resin (PR) as a carbon precursor to produce high-quality laser-induced graphene (LIG) characterized by high crystallinity and low defect density. The fabricated LIG underwent comprehensive characterization using SEM, Raman spectroscopy, XPS, and XRD. Subsequently, we developed strain sensors with a hexagonal honeycomb pattern and temperature sensors with a line pattern based on PR-derived LIG. The strain sensor exhibited an outstanding measurement factor of 4.16 × 10⁴ with a rapid response time of 32 ms, which is applied to detect various movements like finger movements and human pulse. Meanwhile, the temperature sensor demonstrated a sensitivity of 1.49%/°C with a linear response range of 20–50 °C. The PR-derived LIG shows promising potential for applications in human physiological health monitoring and other advanced wearable technologies.