In situ synthesized copper-incorporated laser-induced graphene enabling high-sensitivity flexible temperature sensing

Abstract

Laser-induced graphene (LIG) holds considerable promise for sensing applications due to its unique structure, favorable properties, and low-cost fabrication. However, its negative temperature coefficient (NTC) and relatively low sensitivity have limited its use in temperature sensing compared to other sensing domains. In this work, we employed a one-step laser in situ synthesis method to fabricate copper-incorporated LIG (Cu@LIG), which successfully converts the NTC behavior of pristine LIG into a positive temperature coefficient (PTC) effect. The Cu@LIG/PI composite exhibits a PTC of 0.321% °C⁻¹, in contrast to NTC (−0.047% °C⁻¹) of LIG/PI. By further integrating Cu@LIG with PDMS, the synergistic effect between the material's PTC and the resistance increase caused by PDMS thermal expansion significantly enhances the sensor's sensitivity. The resulting PDMS/Cu@LIG/PDMS sensor demonstrates outstanding temperature-sensing performance over 25–100 °C, with a high temperature coefficient of resistance (TCR) of 9.341% °C⁻¹ and good linearity (R² = 0.98). Segment analysis reveals a further rise in TCR to 11.338% °C⁻¹ in the 55–100 °C range while maintaining excellent linearity (R² = 0.999). The sensor also achieves a temperature resolution of 0.2 °C, along with good cycling stability and insensitivity to humidity. These combined features make it highly suitable for wearable electronics and human–machine interfaces, including applications in respiratory and body temperature monitoring.