Hyo-Chol Sin

Seoul National University, Sŏul, Seoul, South Korea

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Publications (9)6.88 Total impact

  • Young Hoon Lee, Hyo-Chol Sin, Nam Woong Kim
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    ABSTRACT: Slip is well known to take place in micrometer- and nanometer-scale flows. In this study, slip and wall adhesion effects on the imprinting pressure of thermal nanoimprint lithography (NIL) were investigated using computational fluid dynamics. The influence of the mold pattern shape on the imprinting pressure was also analyzed. In thermal NIL, the importance of time in the filling process is relatively high. Reducing the imprinting pressure induces process speed increases, raising productivity a little. Full-slip and no-slip conditions were compared, and various contact angles were applied to survey the influence of the slip condition and wall adhesion, respectively. The full-slip cases required imprinting pressures less than the half values of the no-slip cases. The minimum imprinting pressure was required when the contact angle between the mold and polymer resist was 120°. It was confirmed that the residual thickness decreased as the amount of slip increased, leading to a diminution in the postprocessing time.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2009; 27(2). · 1.36 Impact Factor
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    Nam Woong Kim, Kug Weon Kim, Hyo-Chol Sin
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    ABSTRACT: Squeeze flow theory has been used as an effective tool to clarify how and which process conditions determine cavity-filling behavior in nanoimprint lithography (NIL). Conventional squeeze flow models used in NIL research fields have assumed no-slip conditions at the solid-to-liquid boundaries, that is, at the stamp-to-polymer or polymer-to-substrate boundaries. The no-slip assumptions are often violated, however, in micrometer- to nanometer-scale fluid flow. It is therefore necessary to adopt slip or partial slip boundary conditions. In this paper, an analytical mathematical model for the cavity-filling process of NIL that takes into account slip or partial slip boundary conditions is derived using squeeze flow theory. Velocity profiles, pressure distributions, imprinting forces, and evolutions of residual thickness can be predicted using this analytical model. This paper also aims to elucidate how far the slip phenomenon is able to promote the process rate.
    Microelectronic Engineering - MICROELECTRON ENG. 01/2009; 86(11):2324-2329.
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    Nam Woong Kim, Kug Weon Kim, Hyo-Chol Sin
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    ABSTRACT: Nanoimprint lithography (NIL) is an emerging technology that enables cost-effective and high-throughput nanofabrication. Nevertheless, there are some disadvantages to this method, especially for thermal NIL. A major disadvantage of thermal NIL is the thermal cycle, which requires a significant amount of processing time and limits the throughput. One method to overcome this disadvantage is to reduce the processing temperature. Accordingly, it is necessary to determine the effects on the processing parameters for thermal NIL at reduced temperatures and to optimize the parameters. This requires a clear understanding of the behavior of the polymer material during the thermal NIL process. This work focuses on a temperature range of Tg < T < Tg + 40 °C, in which the polymer displays a semi-molten state behavior; this temperature range is lower than conventionally used for thermal NIL. To understand how the processing conditions of temperature, pressure, pattern density, and initial thickness of the polymer resist are related to the quality of a nanoimprinted pattern, simulations of thin polymer films squeezing into nanocavities during thermal NIL were performed using a two-dimensional viscoelastic finite element analysis taking into account stress relaxation behaviors.
    Microelectronic Engineering 09/2008; 85(9):1858-1865. · 1.22 Impact Factor
  • Nam Woong Kim, Kug Weon Kim, Hyo-Chol Sin
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    ABSTRACT: An optical disk drive is consistently excited by high-speed rotation of a mass-unbalanced disk, which causes vibrations that greatly affect the overall reliability of the reading and writing process. To reduce the vibration, various anti-vibration strategies have been introduced to the optical disk drive industry. One approach is a dynamic vibration absorber. In this paper, the dynamic behavior of a DVDplusmnRW combo drive system with a dynamic vibration absorber was analyzed using a 12 degrees of freedom, rigid, multi-body dynamic model. The effective location and optimal frequency ratio of the dynamic vibration absorber were obtained from the analysis. A dynamic vibration absorber was fabricated based on the analysis and the vibration-reduction performance was confirmed experimentally.
    IEEE Transactions on Consumer Electronics 09/2007; · 1.09 Impact Factor
  • W Y Cho, J K Nam, S M Yun, Hyo-Chol Sin
    Proceedings of The Institution of Mechanical Engineers Part B-journal of Engineering Manufacture - PROC INST MECH ENG B-J ENG MA. 01/2007; 221(5):845-856.
  • Ji‐Geun Nam, Hyo-Chol Sin, Sang‐Sik Na
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    ABSTRACT: Increased application of optical disks has required a rotating disk with more dynamic stability and better optical quality. A new concept of controlling the processing condition of injection molded disks is developed to improve their optical quality and vibration characteristics. To assess the effect of process conditions on residual stresses, birefringence, and critical speed, an orthogonal array for design of experiments is used. Melt temperature, filling speed, and packing pressure were effective parameters, but mold temperature and interactions among process conditions were not. The birefringence and critical speed were affected by the residual stress distribution, which varied according to the distance from the gate and processing condition. Considering the effect of the processing conditions and distance from the gate, we calculated the weight factors on residual stresses along the radial direction. Choosing weighted stress to be the target value for optimization of residual stresses, processing conditions control was accomplished. Under the newly proposed conditions, optical quality and stability of injection molded disk were simultaneously improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3275–3285, 2006
    Journal of Applied Polymer Science 06/2006; 101(5):3275 - 3285. · 1.40 Impact Factor
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    Hyo-Chol Sin, Ji-Geun Nam
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    ABSTRACT: Increased application of optical disks requires more improved dynamic stability of rotating disks. In this study, a new concept of controlling the processing conditions of injection molded disks was developed to improve vibration characteristics. The critical speed, which shows stiffness and dynamic stability of disk, is affected by the residual stress distribution; this varies as functions of distance from the gate and processing condition. The critical speed of disk was calculated with the initial stress taken into consideration, which was determined from injection molding simulation. Choosing melt temperature, mold temperature, filling speed and packing pressure as design parameters, critical speed is maximized with the method of response surface. It is shown that the stability of injection molded disk has been improved for the new condition obtained as a result of the study proposed.
    Transactions of the Korean Society of Mechanical Engineers A 01/2006; 30(6):615-621.
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    ABSTRACT: The hole-type crush initiators according to various ratios of thickness to width (t/b) were studied. And the approximate equation to quickly predict the optimum size of the crush initiator by impact velocity for each ratio of thickness to width was introduced. Also, the simple rectangular and circular dent-type crush initiators of a front frame with non-uniform closed-hat section in a vehicle were studied for frontal crashworthiness according to various ratios of thickness to width (t/b).The optimum size and dent depth of a crush initiator, whose location is decided by the homogenization method, were studied by using design of experiment and response surface method. Design analysis results of the dent-type crush initiators were compared with those of the hole-type crush initiator of the same size as the dent-type crush initiators.The rectangular dent-type crush initiator absorbed more crash energy than the circular dent-type crush initiator. Dynamic mean crushing loads of a rectangular dent-type crush initiator of size equal to that of the hole-type crush initiator designed by the homogenization method were similar to those of the hole-type crush initiator.The trend curve of the optimum size rectangular dent-type crush initiator design is similar with the trend curve of hole-type crush initiator design. Therefore, the approximate equation used to predict the optimum size of the hole-type crush initiator can be applied to find the optimum size of the rectangular dent-type crush initiator.
    Thin-Walled Structures 01/2006; 44(4):415-428. · 1.23 Impact Factor
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    Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering 01/2006; 220(10):1383-1399. · 0.58 Impact Factor