In the 4th industry era, the importance of sensors that provide data to artificial intelligence along with big data and object internet is increasing. Therefore, human wearable healthcare system in the wearable device market has been actively researched for a wearable system made of a flexible material, away from a sensor developed with existing rigid material. When fabricated with a soft material, the user is guaranteed freedom of movement and it is also possible to measure complex body movements that conventional sensors cannot measure.
In this study, the curing characteristics of photocurable polymers for rapid prototyping of flexible sensors using ultraviolet nanosecond pulsed lasers, the change in conductivity due to spray coating of silver nanowires, the change in electrical conductivity due to heat treatment of silver nanowires coated with sprays and the performance of the sensor according to the parameters. the curing characteristics of the photocurable polymer were measured for the laser output, scan speed and line width of the cured line depending on the distance between the lens and the lens for 2D printing. At this time, the cured linewidth value tended to decrease linearly as the output was lower and the scan speed was higher. Based on this, it can be considered that it is possible to select the appropriate hatch interval and scan speed according to the laser output to reduce the molding error on the surface when molding, and to mold with a uniform surface. The silver nanowires used in the experiment of the change of the conductivity according to the spray coating. When the nanowire were linearly increased, the electric conductivity was increased. When the results are compared with the substrate having the central portion of the substrate patterned, the same amount of nanowires were not significantly different in terms of electrical conductivity. we experimented the change of resistance of the silver Nano-wires on the substrate with heat and photo-heat treatment.
In the case of heat treatment using hotplate and laser, the electrical resistance decreased rapidly at 200 °C in the hot plate, but the electrical resistance increased sharply after a certain time. In addition, the wire color on the substrate changed to orange. On the other hand, when the laser was used, the light sintering occurred at 1.3 mW and the resistance decreased. At this time, the decrease rate was slower than 200 °C on the hot plate, but the substrate and the wire were not visibly damaged. When the laser output was 5 mW or higher, the photolithography reaction was observed and the nanowire on the substrate was etched. In this case the color of the nanowire on the substrate gradually became cloudy depending on the laser power. Results of repeated banding with reduced resistance by heat treatment and repeated banding with simple spray coating without heat treatment did not show a significant difference in electrical resistance between the two cases. In the case of silver nano-wires, if the electric conductivity of about 40 Ω is almost no change in electrical resistance due to the band, it can be considered that the sensitivity of the silver Nano wire cannot be measured due to the band. In this case, however, it can be applied to flexible electrodes. As the length increased, the resistance increased, and the resistance returned to its original value when the substrate returned to its original length within a certain range. In addition, GF showed a dependence on the scattered pattern of silver nanowire rather than initial resistance.
Thesis Advisor: Prof. Junyeop Yeo