• Journal of the Korean Chemical Society
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• v.49 no.3
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• pp.292-299
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• 2005

• Polymer(Korea)
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• v.29 no.4
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• pp.418-421
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• 2005

Three-dimensional (3D) microfabrication process using two-photon polymerization (TPP) is developed to fabricate the curved microstructures in a layer, which can be applied potentially to optical MEMS, nano/micro-devices, etc. A 3D curved structure can be expressed using the same height-contours that are defined by symbolic colors which consist of 14 colors. Then, the designed bitmap figure is transformed into a multi-exposure voxel matrix (MVM). In this work a multi-exposure voxel matrix scanning method is used to generate various heights of voxels according to each laser exposure time that is assigned to the symbolic colors. An objective lens with a numerical aperture of 1.25 is employed to enlarge the variation of a voxel height in the range of 1.2 to 6.4 um which can be controlled easily using the various exposure time. Though this work some 3D curved micro-shapes are fabricated directly to demonstrate the usefulness of the process without a laminating process that is generally required in a micro-stereolithography process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.999-1005
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• 2004

A new stamp fabrication technique for the soft lithography has been developed in the range of several microns by means of a nano-replication printing (nRP) process. In the nRP process, a figure or a pattern can be replicated directly from a two-tone bitmap figure with nano-scale details. A photopolymerizable resin was polymerized by the two-photon absorption which was induced by a femtosecond laser. After the polymerization of master patterns, a gold metal layer (about 30 ㎚ thickness) was deposited on the fabricated master patterns for the purpose of preventing a join between the patterns and the PDMS, then the master patterns were transferred in order to fabricate a stamp by using the PDMS (poly-dimethylsiloxane). In the transferring process, a few of gold particles, which were isolated from the master patterns, remained on the PDMS stamp. A gold selective etchant, the potassium iodine (KI) was employed to remove the needless gold particles without any damage to the PDMS stamp. Through this work, the effectiveness of the nRP process with the PDMS molding was evaluated to make the PDMS stamp with the resolution of around 200 ㎚.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.6
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• pp.160-166
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• 2004

In this study, a new algorithm, named as Contour Offset Algorithm(COA) is developed to fabricate precise features or patterns in the range of several micrometers by nano replication printing(nRP) process. In the nRP process, a femto-second laser is scanned on a photosensitive monomer resin in order to induce polymerization of the liquid monomer according to a voxel matrix which is transformed from the bitmap format file. After polymerization, a droplet of ethanol is dropped to remove the unnecessary remaining liquid resin and then only the polymerized figures with nano-scaled precision are remaining on the glass plate. To obtain more precise replicated features, the contour lines in voxel matrix should be modified considering a voxel size. In this study, the efficiency of the proposed method is shown through two examples in view of accuracy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.41-41
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• 2003

• Proceedings of the Optical Society of Korea Conference
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• 2004.07a
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• pp.188-189
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• 2004

• Journal of the Korean Society for Precision Engineering
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• v.22 no.10 s.175
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• pp.17-25
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• 2005

• Journal of the Korean Society for Precision Engineering
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• v.26 no.8
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• pp.119-125
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• 2009

Fabrication of a three-dimensional (3D) metallic mold for multi-production of a microstructure was studied to settle the problem of long processing time in 3D microfabrication. To date, complicated 3D microstructures including 3D photonic crystals, 3D microlens array, 3D filter for microfludics, and something else were created successfully using the two-photon polymerization (TPP) which was considered as paving the way to fabricate a real 3D shape in nano/microscale. However, for those fabrications, much processing time and efforts were inevitably required. To solve this issue, a simple and effective way was proposed in this paper; 3D master patterns were prepared using TPP, and then counter-shaped Ni molds were fabricated by electroforming process. By using these molds, 3D microstructures can be reproduced with short-processing time and low-effort comparing to the conventional approach, TPP We report some parameters to fabricate a metallic mold precisely.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.3 s.180
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• pp.156-162
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• 2006

Direct fabrication of nano patterns has been studied employing a nano-stereolithography (NSL) process. The needs of nano patterning techniques have been intensively increased for diverse applications for nano/micro-devices; micro-fluidic channels, micro-molds. and other novel micro-objects. For fabrication of high-aspect-ratio (HAR) patterns, a thick spin coating of SU-8 process is generally used in the conventional photolithography, however, additional processes such as pre- and post-baking processes and expansive precise photomasks are inevitably required. In this work, direct fabrication of HAR patterns with a high spatial resolution is tried employing two-photon polymerization in the NSL process. The precision and aspect ratio of patterns can be controlled using process parameters of laser power, exposure time, and numerical aperture of objective lens. It is also feasible to control the aspect ratio of patterns by truncation amounts of patterns, and a layer-by-layer piling up technique is attempted to achieve HAR patterns. Through the fabrication of several patterns using the NSL process, the possibility of effective patterning technique fer various N/MEMS applications has been demonstrated.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.12
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• pp.136-142
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• 2007

Precise fabrication of three-dimensional (3D) self-standing microstructures on thin glass plates via two-photon induced polymerization (TPP) has been an important issue for innovative 3D nanodevices and microdevices. However, there are still issues remaining to be solved, such as building 3D microstructures on opaque materials via TPP and being able to implant them as functional parts onto practical systems. To settle these issues simply and effectively, we propose a contact print lithography (CPL) method using an ultraviolet (UV)-curable polymer layer. We report some of the possibilities and potential of CPL by presenting our results for transplanting 3D microstructures onto large-area substrates and also our examination of some of the effects of the process parameters on successful transplantation.