High-Resolution Femtosecond Laser-Induced Carbon and Ag Hybrid Structure for Bend Sensing

Miniaturized resistance-based portable bending sensors have been widely used for human health monitoring in recent years. Their sensitivities are defined by their resistance variations (ΔR/R), which strongly rely on the conductivity and minimum line width of the sensing unit. Laser-induced carbonization is a fast and simple method to fabricate porous-sensing structures. However, the fabrication resolution of conductive and deformation-sensitive structures is limited by the thermal effect of commonly used laser sources. With the assistance of femtosecond laser temporal shaping, plasma ejection confinement, and silver nitrate doping, the sheet resistance of the sensing structure was improved from 15 to 0.0004 Ω/□. A thin line with a lateral resolution of 6.5 μm is fabricated as the sensing unit. The fFabricated structures are characterized by electron microscopy, Raman spectroscopy, energy-dispersive spectroscopy, X-ray scattering, and time-resolved images. The strain sensor demonstrates a ΔR/R of 25.8% with a rising edge of 109 ms in the cyclic bending test. The sensor is further applied for detecting human pulse and finger bending.