• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.10 s.241
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• pp.1298-1306
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• 2005

In this paper, Part II, we realized the Serpentine Laminating Micromirer (SLM) which was proposed in the accompanying paper, Part I, by means of the injection molding process in mass production. In the SLM, the higher level of chaotic mixing can be achieved by combining two general chaotic mixing mechanisms of splitting/recombination and chaotic advection by the successive arrangement of 'F'-shape mixing units in two layers. Mold inserts for the injection molding process of the SLM were fabricated by SU-8 photolithography and nickel electroplating. The SLM was realized by injection molding of COC (cyclic olefin copolymer) with the fabricated mold inserts and thermal bonding of two injection molded COC substrates. To compare the mixing performance, a T-type micromixer was also fabricated. Mixing performances of micromixers were experimentally characterized in terms of an average mixing color intensity of a pH indicator, phenolphthalein. Experimental results show that the SLM has much better mixing performance than the I-type micromixer and chaotic mixing was successfully achieved from the SLM over the wide range of Reynolds number (Re). The chaotic micromixer, SLM proposed in this study, could be easily integrated in Micro-Total-Analysis- System , Lab-on-a-Chip and so on.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.1
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• pp.15-21
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• 2008

SiC has an excellent resistance to oxidation and corrosion, high temperature strength and good thermal conductivity. However, it is difficult to density because of its highly covalent bonding characteristics. Hot-press sintering process was applied to fabricate fully densified SiC ceramics with carbon and boron addition as a sintering additive. The addition of carbon improved the mechanical properties of SiC because it could induce a fine and homogeneous microstructure by the suppression of abnormal growth of SiC grain. Also, the addition of carbon could control the phase transformation of SiC. The phase transformation of 6H to 4H increased with sintering temperature but the addition of carbon decreased that kind of phase transformation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.3
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• pp.109-114
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• 2016

Monodispersed $ZnGa_2O_4$ microspheres were synthesized by a facile two-step process consisting of a solvothermal method and calcination process. The prepared monodispersed $ZnGa_2O_4$ microspheres were aggregated into 3D microstructures by self-assembly with a large number of small $ZnGa_2O_4$ particles generated in nucleation. This nucleation and self-assembly making hierarchical microstructures were depended on the concentration of PEG (polyethylene glycol) due to CAC (critical aggregation concentration) theory. And also we controlled the amount of zinc acetate to make pure $ZnGa_2O_4$ phase. Additionally, to fix the optimized calcination condition, sample was characterized by TG-DTA to prove the thermal property in the calcination process and by FT-IR to identify the changes of functional group bonding between each element of the $ZnGa_2O_4$ precursor and oxide calcined at $900^{\circ}C$ for 1 h.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.1
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• pp.11-19
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• 2003

A micro sensor array with 4 discrete sensors integrated on a microhotplate was developed for identifying the kinds and quantities of explosive gases. The sensor array consisited of four tin oxide-based thin films with the high and broad sensitivity to the tested explosive gases and uniform thermal distribution on the plate. The microhotplate, using silicon substrate with N/O/N membrane, dangling in air by Al bonding wires, and controlling the thickness by chemical mechanical process (CMP), has been designed and fabricated. By employing the sensitivity signal of the sensor array at 40$0^{\circ}C$, we could reliably classily the kinds and quantities of the explosive gases like butan, propane, LPG, and carbon monoxide within the range of threshold limit values (TLVs), employing principal component analysis (PCA).

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.69-74
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• 2017

Effect of post-annealing treatment times at $200^{\circ}C$ on the peel strength of screen-printed Ag film/polyimide substrate were systematically investigated by $180^{\circ}$ peel test for thermal reliability assessment of printed interconnect. Initial peel strength around 16.7 gf/mm increased up to 29.4 gf/mm after annealing for 24hours, and then sharply decreased to 22.3, 3.6, 0.6, and 0.1 gf/mm after 48, 100, 250, and 500 hours, respectively. Ag-O-C chemical bonding as well as binder organic bridges formations seemed to be responsible for interfacial adhesion improvement after the initial annealing treatment, while excessive Cu oxide formation at Cu/Ag interface seems to be closely related to sharp decrease in peel strength for longer annealing times.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.168-171
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• 2017

In this study, we observed degradation mechanism of FKM O-ring by X-ray photoelectron spectroscopy(XPS) at atmosphere condition. FKM O-ring had 3.53mm of cross-sectional diameter and 91.67mm of inner diameter. After thermal degradation, oxygen atom concentration of FKM O-ring was increased to 20.39%, and fluorine atom concentration was decreased to 8.29%. We observed that degradation reaction occurred by oxidation reaction. By C1s and F1s peak analysis, we confirmed that oxidation reaction usually occurred at C-F bonding of FKM main chain. Also, carboxyl group(C-OH, C=O, O=C-O) produced by oxidation reaction from O1s peak analysis.

• Journal of Sensor Science and Technology
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• v.17 no.5
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• pp.369-374
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• 2008

A novel fiber optic surface plasmon resonance (SPR) sensor using cyclic olefin copolymer (COC) prism with the spectral modulation is presented. The SPR sensor chip is fabricated using the SU-8 photolithography, Ni-electroplating and COC injection molding process. The sidewall of the COC prism is partially deposited with Au/Cr (45/2.nm thickness) by e-beam evaporator, and the thermal bonding process is conducted for micro fluidic channels and optical fibers alignment. The SPR spectrum for a phosphate buffered saline (0.1.M PBS, pH.7.2) solution shows a distinctive dip at 1300.nm wavelength, which shifts toward longer wavelength with respect to the bovine serum albumin (BSA)concentrations. The sensitivity of the wavelength shift is $1.16\;nm{\cdot}{\mu}g^{-1}{\cdot}{\mu}l^{-1}$. From the wavelength of SPR dips, the refractive indices (RI) of the BSA solutions can be theoretically calculated using Kretchmann configuration, and the change rate of the RI was found to be $2.3{\times}10^{-5}RI{\cdot}{\mu}g^{-1}{\cdot}l^{-1}$. The realized fiber optic SPR sensor with a COC prism has clearly shown the feasibility of a new disposable, low cost and miniaturized SPR biosensor for biochemical molecular analyses.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.174-174
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• 2010

Gallium Nitride(GaN) attracts great attention due to their wide band gap energy (3.4eV), high thermal stability to the solid state lighting devices like LED, Laser diode, UV photo detector, spintronic devices, solar cells, sensors etc. Recently, researchers are interested in synthesis of polycrystalline and amorphous GaN which has also attracted towards optoelectronic device applications significantly. One of the alternatives to deposit GaN at low temperature is to use Single Source Molecular Percursor (SSP) which provides preformed Ga-N bonding. Moreover, our group succeeds in hybridization of SSP synthesized GaN with Single wall carbon nanotube which could be applicable in field emitting devices, hybrid LEDs and sensors. In this work, the GaN thin films were deposited on c-axis oriented sapphire substrate by MBE (Molecular Beam Epitaxy) using novel single source precursor of dimethyl gallium azido-tert-butylamine($Me_2Ga(N_3)NH_2C(CH_3)_3$) with additional source of ammonia. The surface morphology, structural and optical properties of GaN thin films were analyzed for the deposition in the temperature range of $600^{\circ}C$ to $750^{\circ}C$. Electrical properties of deposited thin films were carried out by four point probe technique and home made Hall effect measurement. The effect of ammonia on the crystallinity, microstructure and optical properties of as-deposited thin films are discussed briefly. The crystalline quality of GaN thin film was improved with substrate temperature as indicated by XRD rocking curve measurement. Photoluminescence measurement shows broad emission around 350nm-650nm which could be related to impurities or defects.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1054-1057
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• 2004

The nitrogenated diamond-like carbon (NDLC) exhibits high electrical resistivity and thermal conductivity that are similar to the properties shown by diamond-like carbon (DLC) films. These diamond-like transparent properties in NDLC come in a material consisting of $sp^2$-bonded carbon versus the $sp^3$-carbon of DLC. The diamond-like properties and nondiamond-like bonding make NDLC an attractive candidate for applications. Liquid crystal (LC) alignment capabilities with ion beam exposure on NDLC thin films and electro-optical (EO) performances of the ion-beam-aligned twisted nematic liquid crystal display (TN-LCD) with oblique ion beam exposure on the NDLC thin film surface were studied. An excellent uniform alignment of the nematic liquid crystal (NLC) alignment with the ion beam exposure on the NDLC thin films was observed. In addition, it can be achieved that the good EO properties of the ion-beam-aligned TN-LCD. Finally, we will present the residual DC property of the ion-beam-aligned TN-LCD on the NDLC thin film surface.

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.775-783
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• 2012

The effect of thermal annealing on the in-situ growth characteristics of intermetallics (IMCs) and the mechanical strength of Cu pillar/Sn-3.5Ag microbumps are systematically investigated. The $Cu_6Sn_5$ phase formed at the Cu/solder interface right after bonding and grew with increased annealing time, while the $Cu_3Sn$ phase formed at the $Cu/Cu_6Sn_5$ interface and grew with increased annealing time. IMC growth followed a linear relationship with the square root of the annealing time due to a diffusion-controlled mechanism. The shear strength measured by the die shear test monotonically increased with annealing time. It then changed the slope with further annealing, which correlated with the change in fracture modes from ductile to brittle at a critical transition time. This is ascribed not only to the increasing thickness of brittle IMCs but also to the decreasing thickness of the solder, as there exists a critical annealing time for a fracture mode transition in our thin solder-capped Cu pillar microbump structures.