[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 03/2009; 27(2). DOI:10.1116/1.3089324 · 1.36 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: A solver based on the Hele-Shaw model can perform calculations faster than a full three-dimensional (3D) solver, but it has a drawback: it requires a mid-plane mesh whose transformation is considerably time consuming. To overcome this drawback, a new solver based on the Hele-Shaw model was developed. The new solver can directly read a 3D tetra mesh made from computer-aided design (CAD) models and perform the filling analysis of injection moulding quickly with reliable accuracy. In the current study, some classification and assignment operations are performed to apply the 3D mesh to the new solver based on mid-plane mesh. In addition, a node-pairing method is proposed for fast filling analysis. For verification of this method, results of this study were compared with those of MPI, which is one of the products of Moldflow. The results from the developed solver for most cases were very similar to those of MPI, and the analysis took only 30-40 per cent of the time consumed by MPI.
Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture 05/2007; 221(5):845-856. DOI:10.1243/09544054JEM725 · 0.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nanoimprint lithography (NIL) is an emerging technology enabling cost-effective and high-throughput nanofabrication. To successfully imprint a nano-sized pattern, the process conditions such as temperature, pressure, and time should be appropriately selected. This starts with a clear understanding of polymer material behavior during the NIL process. In this work, the squeezing of thin polymer films into nanocavities during the thermal NIL has been investigated based upon a two-dimensional viscoelastic finite element analysis in order to understand how the process conditions affect a pattern quality. The simulations have been performed within the viscoelastic plateau region and the stress relaxation effect has been taken into account.
[Show abstract][Hide abstract] ABSTRACT: The dynamic loads imposed on suspension components during vehicle driving are transferred through bushings and joints. The loads from bushings are important factors in the prediction of the fatigue life of a component and the dynamic characteristics of a vehicle. In this paper, the linear characteristic of a bushing is approximated by finite element analysis and applied to a multi-body dynamic model of the vehicle. The influence of bushing compliance is investigated, considering the dynamically responsive stress of the lower control arm in a virtual proving ground test. With the bushing compliance of the front suspension as a design parameter, the Taguchi method is used in the systematic process of a robust design to reduce the stress value of the lower control arm.
Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering 10/2006; 220(10):1383-1399. DOI:10.1243/09544070JAUTO101 · 0.83 Impact Factor
[Show abstract][Hide abstract] 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 06/2006; 30(6):615-621. DOI:10.3795/KSME-A.2006.30.6.615
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: In high-speed optical disk drive, the excitation caused by rotation of a mass-unbalanced disk is a major source of vibration. The vibration can be a disturbance to the servo system, which is sufficient to cause severe failures in the reading and writing process. The vibration also causes users to feel unpleasantness. The vibration reduction is therefore essential for the reliable operation of optical disk drive. One of the approaches to reduce the vibration is a dynamic vibration absorber(DVA). In this paper, we analyze the dynamic behavior of combo drive system with DVA through 12-dof rigid multi-body dynamic model. The effective location and the optimal frequency ratio for the DVA are obtained from the analysis. The DVA are fabricated based on the analysis and its usefulness is confirmed. ??