Journal of the Korean Society for Precision Engineering

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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Process for the Fabrication of Nickel Material High Aspect-ratio Digital PCR Partition: GeeHong Kim, HyungJun Lim, SoonGeun Kwon, Hak-Jong Choi; J. Korean Soc. Precis. Eng. 2024;41(8):663-668.
Published online August 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.059

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This paper outlines the fabrication process of the partition component, a crucial element in digital PCR. The partition component consists of thousands of micro-wells capable of holding small volumes of reagents. In this study, the partition component was created in a honeycomb structure, with hexagonally shaped micro-wells measuring 100 μm in size and spaced 20 μm apart. The fabrication process involved using photolithography, lift-off, and electroplating techniques. Photolithography and lift-off processes were employed to create a pattern of Cu metal layers in a hexagonal honeycomb arrangement on a glass substrate. Subsequently, the Cu metal-patterned substrate was used to produce pillar patterns of SU-8 with a high aspect ratio using photolithography. Finally, the gaps between the SU-8 pillar patterns were filled with nickel through electroplating, completing the partition component. The micro-wells in the partition component were designed to have an aspect ratio of 4-5; however, in this study, micro-wells with an aspect ratio of 2 and a depth of 200 μm were fabricated.

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Improvement of Synthesis Process for High Aspect Ratio Copper Nanowires via EDA-Mediated Method: Duong Thanh Hung, Hyun Chul Kim; J. Korean Soc. Precis. Eng. 2018;35(5):545-550.
Published online May 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.5.545

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There are two well-known synthetic approaches for copper nanowires (CuNWs): ethylenediamine (EDA)-mediated synthesis and alkylamine-mediated synthesis. The alkylamine-mediated synthesis produces very high aspect ratio nanowires but requires an autoclave for high-pressure environments, and a long reaction time, which normally is above 12 hours. The EDA-mediated synthesis can be carried out under normal conditions and requires 30 min. The CuNWs produced by this method have an average aspect ratio lower than 1000 and are produced in a lower yield. In this paper, the researchers present a modified EDA-mediated synthesis to improve the yield and reduce the synthesis time. When NaOH and Cu(NO3)2 were replaced with KOH and CuCl2, respectively and the reaction temperature was kept at room temperature, the synthesis time was shortened to 15 min. Moreover, the aspect ratio of the as-synthesized Cu NWs increased to 650 and the synthesis yields raised from 17.73% to 80.16%.