Journal of the Korean Society for Precision Engineering

"Woo Young Kim"

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Study on UV Energy Effects in High Aspect Ratio Patterning via the Self-propagating Photopolymer Waveguide (SPPW) Method: Jun Ho Song, Woo Young Kim, Seungwoo Shin, Seok Kim, Young Tae Cho; J. Korean Soc. Precis. Eng. 2025;42(9):757-762.
Published online September 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.041

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This study quantitatively examines the impact of ultraviolet (UV) intensity and energy on the formation of high aspect ratio (HAR) microstructures using the Self-Propagating Photopolymer Waveguide (SPPW) process. This mechanism relies on the self-focusing of UV light within a refractive index gradient, allowing the light to propagate and polymerize vertically beyond the initial exposure zone. Experiments were performed at UV intensities of 7.5, 12.5, and 17.5 mW/cm², with energy levels ranging from 0.0375 to 13.5 J/cm². The results indicated that a lower UV intensity of 7.5 mW/cm² produced uniform and vertically elongated structures, achieving a maximum aspect ratio of 12.26 at 0.9 J/cm². In contrast, higher UV intensities led to lateral over-curing, base expansion, and shape distortion, primarily due to rapid polymerization and the oxygen inhibition effect. These findings emphasize the importance of precisely controlling both UV intensity and energy to produce uniform, vertically aligned HAR microstructures, offering valuable insights for optimizing the SPPW process in future microfabrication applications.

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Finding Ways to Deform Fine Patterns Fabricated by UV Curable Resin: Woo Young Kim, Su Hyun Choi, Seonjun Kim, Young Tae Cho; J. Korean Soc. Precis. Eng. 2020;37(4):291-296.
Published online April 1, 2020; DOI: https://doi.org/10.7736/JKSPE.019.141

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In this study, experiments were performed to determine if the pattern fabricated by the UV nano imprint process could be modified using additional processes such as surface treatment. We wanted to confirm the fabrication possibility of a special pattern such as the reverse trapezoidal shape difficult to produce because of the releasing problem. The UV ozone treatment (Hydrophilic Treatment) and OTS coating (Water Repellent Treatment) were used and shape modification occurred under controlled treatment time. As a result of performing the UV ozone treatment for 30 minutes or more on a micro pattern manufactured by UV curing resin of PUA series, the contraction phenomenon of the micro structure occurred and the shrinkage was dependent on treatment time. When the OTS treatment was performed, the surface of the microscale pattern could be roughened. When the nanoscale pattern was treated, the pattern change could be induced. It was possible to partially cure the resin by adjusting the UV absorption using dye material, and the deformation of the pattern was made by an additional pressing process. As a result of the experiment of the various methods causing the shape change of the cured pattern, the possibility of the methods was verified.