Abstract
A laser-induced-graphene (LIG) pattern fabricated using a 355 nm pulsed laser was applied to a strain sensor. Structural analysis and functional evaluation of the LIG strain sensor were performed by Raman spectroscopy, scanning electron microscopy (SEM) imaging, and electrical–mechanical coupled testing. The electrical characteristics of the sensor with respect to laser fluence and focal length were evaluated. The sensor responded sensitively to small deformations, had a high gauge factor of ~160, and underwent mechanical fracture at 30% tensile strain. In addition, we have applied the LIG sensor, which has high sensitivity, a simple manufacturing process, and good durability, to human finger motion monitoring.
Highlights
Irradiation of a laser onto polyimide film at a certain degree of laser fluence, i.e., the optical energy delivered per unit area, resulted in photothermal ablation by the locally high temperature, which breaks the chemical bonds of the polyimide film; this process has been reported to produce laser-induced graphene (LIG) with a porous multilayer structure [11,20,21,22]
A 25 μm-thick polyimide film was used to better implant the LIG pattern in PDMS; the degrees of implantation and carbonization were evaluated according to laser fluence
The carbonization of the LIG pattern is mainly due to photothermal ablation [20,28,29]; the of carbonization depends on laser parameters such as laser power, scanning speed, and focal length
Summary
Metal wires, carbon nanotubes, and graphene have been applied to substrates such as polyethyleneimine (PEI), polyethylene terephthalate (PET), ECOFLEX, and polydimethylsiloxane (PDMS); the resulting materials are mechanically flexible and robust, and are used in many areas such as touch screens, biomedical devices, wearable devices, human–robot interfaces, solar cells, and supercapacitors [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Irradiation of a laser onto polyimide film at a certain degree of laser fluence, i.e., the optical energy delivered per unit area, resulted in photothermal ablation by the locally high temperature, which breaks the chemical bonds of the polyimide film; this process has been reported to produce LIG with a porous multilayer structure [11,20,21,22]. Other strain sensors have been reported that have a piezoresistive effect that overcomes the shortcomings of conventional sensors; these sensors combine an elastomer and a material with a multidimensional structure, such as graphene or carbon nanotubes (CNTs). Despite many attempts to fabricate strain sensors that use sensitive, high-performance nanoparticles, such as CNT and graphene, previous research on sensors has led to good sensitivity and mechanical performance but was unsuccessful in making the fabrication process easier or in reducing the fabrication costs. Structural analysis of the LIG pattern according to the laser fluence and laser focal length, as well as evaluation of device applicability as a sensor, is performed
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