• Macromolecular Research
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• v.14 no.5
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• pp.559-564
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• 2006

The improvement of spatial resolution is a fundamental issue in the two-photon, polymerization-based, laser writing. In this study, a voxel tuning method using a radical quencher was proposed to increase the resolution, and the quenching effect according to the amount of radical quencher was experimentally investigated. Employing the proposed method, the lateral resolution of the line patterns was improved almost to 100 nm. However, a shortcoming of the quenching effect was the low mechanical strength of polymerized structures due to their short chain lengths. Nano-indentation tests were conducted to evaluate quantitatively the relationship between mechanical strength and the mixture ratio of the radical quencher into the resins. The elastic modulus was dramatically reduced from an average value of 3.015 to 2.078 GPa when 5 wt% of radical quencher was mixed into the resin. Three-dimensional woodpile structures were fabricated to compare the strength between the resin containing radical quencher and the original resin.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.4
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• pp.303-309
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• 2008

Dense and fine polymer patterns often collapse, as they come into contact with each other at their protruding tips. Resist pattern collapse depends on the aspect ratio of patterns and the surface tension of rinsing materials. The pattern collapse is a very serious problem in microfabrication, because it is one of the factors which limit the device dimensions. The reasons for the pattern collapse are known as the surface tension of rinse liquid, centrifugal force and rinse liquid flow produced in the developing process. In this work, we tried to evaluate the pattern collapse of three-dimensional microstructures that were fabricated by two-photon induced photopolymerization, and showed the way how to reduce the deformation of microstructures.

• Bulletin of the Korean Chemical Society
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• v.25 no.8
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• pp.1119-1120
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• 2004

• Journal of the Korean Society for Precision Engineering
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• v.23 no.11 s.188
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• pp.7-16
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• 2006

• Macromolecular Research
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• v.14 no.2
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• pp.245-250
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• 2006

• Polymer(Korea)
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• v.28 no.4
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• pp.305-313
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• 2004

A vacuum pressure-difference technique for making a nano-precision replica is investigated for various applications. Master patterns for replication were fabricated using a nano-replication printing (nRP) process. In the nRP process, any picture and pattern can be replicated from a bitmap figure file in the range of several micrometers with resolution of 200nm. A liquid-state monomer is solidified by two-photon absorption (TPA) induced by a femto-second laser according to a voxel matrix scanning. After polymerization, the remaining monomers were removed simply by using ethanol droplets. And then, a gold metal layer of about 30nm thickness was deposited on the fabricated master patterns prior to polydimethylsiloxane molding for preventing bonding between the master and the polydimethylsiloxane mold. A few gold particles attached on the polydimethylsiloxane stamp during detaching process were removed by a gold selecting etchant. After fabricating the polydimethylsiloxane mold, a nano-precision polydimethylsiloxane replica was reproduced. More precise replica was produced by the vacuum pressure-difference technique that is proposed in this paper. Through this study, direct patterning on a glass plate, replicating a polydimethylsiloxane mold, and reproducing polydimethylsiloxane replica are demonstrated with a vacuum pressure-difference technique for various micro/nano-applications.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.264-267
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• 2005

A subregional slicing method (SSM) is proposed to increase the nanofabrication efficiency of a nano-stereolithography (NSL) process based on two-photon polymerization (TPP). The NSL process can be used to fabricate 3D microstructures via the accumulation of layers of uniform thickness; hence, the precision of the final 3D microstructure depends on the layer thickness. The use of a uniform layer thickness means that, to fabricate a precise microstructure, a large number of thin slices is inevitably required. leading to long processing times. In the SSM proposed here, however, the 3D microstructure is divided into several subregions on the basis of the geometric slope, and then each of these subregions is uniformly sliced with a layer thickness determined by the geometric slope characteristics of each subregion. Subregions with gentle slopes are sliced with thin layer thicknesses, whereas subregions with steep slopes are sliced with thick layer thicknesses. Here, we describe the procedure of the SSM based on TPP, and discuss the fabrication efficiency of the method through the fabrication of a 3D microstructure.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.2
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• pp.210-217
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• 2004

In this study, a new process, named as nano replication printing(nRP) process, is developed for printing any figure in the range of several micrometers by using voxel matrix scanning scheme. In this newly developed process, a femto-second laser is scanned on a photosensitive monomer resin in order to induce polymerization of the liquid resin according to a voxel matrix which is transformed from bitmap format file. After the polymerization, a droplet of ethanol is dropt to remove the unnecessary remaining liquid resin and then the polymerized figures with nano-scaled precision are only remaining on the glass plate. By the nRP process, any figure file of bitmap format could be reproduced as nano-scaled precision replication in the range of several micrometers. Also, nano/micro-scaled patterns for an extremely wide range of applications would become a technologically feasible reality. Some of figures with nano-scaled precision were printed in scaled replication as examples to prove the usefulness of this study.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.3
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• pp.180-187
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• 2004

The miniaturization technologies are perceived as potential key technologies of the future. They will bring about completely different ways in which people and machines interact with the physical world. However, at the present time, the primary technologies used fur miniaturization are dependent on the microelectronic fabrication techniques. The principal shortcomings associated with such techniques are related to the inability of to produce arbitrary three-dimensional features not only in electronics but also in a wide range of metallic materials. In this paper, a ultramicro-stereolithography system assisted with a femto-second laser was developed to fabricate the arbitrary three-dimensional nano/micro-scaled features. In the developed process, a femto-second laser is projected according to CAD data on a photosensitive monomer resin, it induces polymerization of the liquid resin. After the polymerization, a droplet of ethanol is dropped to remove the liquid resin and then the polymerized nano-scaled features only remain. By a newly developed process, miniature devices for an extremely wide range of applications would become a technologically feasible reality. Some of nano/micro-scaled features as examples were fabricated to prove the usefulness of this study at the fundamental stage.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.1
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• pp.45-49
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• 2006

A nano-stereolithography (NSL) process has been developed for the fabrication of three-dimensional (3D) micro-devices with high spatital resolution of approximately 100 nm. In the NSL process, a complicated 3D structure can be created by stacking layer-by-layer, so it does not require any sacrificial layer or any supporting structure. A laminated layer was fabricated by means of solidifying liquid-state monomers using two-photon absorption (TPA) which was induced by a femtosecond laser. When the fabrication of a 3D stacked structure was finished, unsolidified liquid resins were rinsed by ethanol to develop the fabricated structures; then, the polymerized structure was only left on the glass substrate. Through this work, several 3D microstructures such as a micro-channel, shell structures, and photonic crystals were fabricated to evaluate the possibility of the developed system.