• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.6
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• pp.348-352
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• 2016

In this paper, GaN film was grown on AlN/PSS by hydride vapor phase epitaxy compared with GaN on planar sapphire. Thin AlN layer for buffer layer was deposited on patterned sapphire substrate (PSS) by metal organic chemical vapor deposition. Surface roughness of GaN/AlN on PSS was remarkably decreased from 28.31 to 5.53 nm. Transmittance of GaN/AlN grown on PSS was lower than that of planar sapphire at entire range. XRD spectra of GaN/AlN grown on PSS corresponded the wurzite structure and c-axis oriented. The full width at half maximum (FWHM) values of ${\omega}$-scan X-ray rocking curve (XRC) for GaN/AlN grown on PSS were 196 and 208 arcsec for symmetric (0 0 2) and asymmetric (1 0 2), respectively. FWHM of GaN on AlN/PSS was improved more than 50% because of lateral overgrowth and AlN buffer effect.

• Journal of Sensor Science and Technology
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• v.22 no.5
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• pp.333-337
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• 2013

This study proposes a simply fabricated micro stator for higher output power than previously reported micro stators. The stator has been fabricated by inserting enamel coil in silicon mold formed by micro etching process. The most merits of the proposed micro stator are the simple fabrication process and high output power. Previously reported micro stators have high resistance because the micro coil is fabricated by relatively thin-film-based deposition process such as sputtering and electroplating. In addition, the previously reported micro coil has many electrical contact points for forming the coil structure. These characteristics of the micro stator can lead to low performance in output power. However, the proposed micro stator adopts commercially available enamel coil without any contact point. Therefore, the enamel coil of the proposed micro stator has low junction resistance due to the good electrical quality compared with the deposited or electroplated metal coil. Power generation tests were performed and the fabricated stator can produce 5.4 mW in 4000 RPM, $1{\Omega}$ and 0.3 mm gap. The proposed micro stator can produce larger output power than the previously reported stator spite of low RPM and the larger gap between the permanent magnet and the stator.

• Journal of Sensor Science and Technology
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• v.29 no.6
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• pp.407-411
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• 2020

In this study, we propose an array-type gas sensor with high selectivity and response using multiple oxide semiconductors. The sensor array was composed of SnO₂ and In₂O₃, and the detection characteristics were improved by using Pt, Au, and Pd catalysts. All samples were deposited directly on the Pt interdigitated electrode (IDE) through the e-beam evaporator glancing angle deposition (GAD) method. They grew in the form of well-aligned nanorods at off-axis angles. The prepared SnO₂ and In₂O₃ nanorod samples were exposed to CH₃COCH₃, C₇H₈, and NO₂ gases in a 300℃ dry condition. Au-decorated SnO₂, Au-decorated In₂O₃, and Pd-decorated In₂O₃ exhibited high selectivity for CH₃COCH₃, C₇H₈, and NO₂, respectively. They demonstrated a high detection limit of the sub ppb level computationally. In addition, measurements from each sensor were executed in the 40% relative humidity condition. Although there was a slight reduction in detection response, high selectivity and distinguishable detection characteristics were confirmed.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.7-14
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• 2003

The precious-meta] mineralization of epithermal type in the Korean Peninsula, which is spread over a broader range of ca. 110 to 60 Ma with a major population between 90 and 70 Ma, mainly occurred along the NE-trending major strike-slip fault systems (i.e., the Gongju and Gwangju ones) that commonly include volcano-tectonic depressions and calderas. The occurrence of epithermal mineralization during Late Cretaceous clearly indicates that the geologic setting of the Korean Peninsula changed to the favorable depth of ore formation with very shallow-crustal environments (〈1.0 kb) accompanied with gold-silver (-base-meta]) mineralization. Epithermal gold-silver deposits in Korea are primarily distinguished as sediment-dominant and volcanic-dominant basins by using criteria of varying alteration, ore and gangue mineralogy deposited by the interaction of different ore-forming fluids with host rocks and meteoric waters. These differences between the central and southern portions are causally linked to the tectonic evolution of the Peninsula during the Cretaceous time. In the Early Cretaceous, the sinistral strike-slip movements due to the oblique subduction of the Izanagi Plate resulted in the Gongju and Gwangju fault systems in the central portion of the Korean Peninsula, which was accompanied with a number of sediment-dominant basins formed along these faults. During the Late Cretaceous, the mode of convergence of the Izanagi Plate changed to northwesteward so that orthogonal convergence occurred with a calc-alkaline volcanism. As results, volcanic-dominant basins were developed in the southern portion of the Peninsula, accompanied with volcano-tectonic depressions and caldera-related fractures. The magmatism and related fractures during Late Cretaceous may play an important role in the formation of geothermal systems. Thus, such fault zones may be favorable environments for veining emplacement that is closely related to the precious-metal mineralization of epithermal type in the Korean Peninsula.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.1 no.1
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• pp.37-42
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• 2000

Copper thin films have been prepared by a metal organic chemical vapor deposition (MOCVD) technology on polyimide and TiN substrates. The Cu-MOCVD technology has advantages of the high deposition rate and the good step coverage compared with the conventional physical vapor deposition (PVD) technology in several industrial applications. The Cu films have been deposited with varying the experimental conditions of substrate temperatures and copper source vapor pressures. The films were annealed in a vacuum condition after the deposition, and the annealing effect on the electrical properties of the films was measured. The crystallinity and the microstructures of the films were observed by scanning electron microscopy (SEM), and the electrical resistivity was measured by 4-point probe. In the case of the Cu deposition on TiN substrate, the best electrical property of the films was measured for the samples prepared at 18$0^{\circ}C$. Very high deposition rate of the Cu film up to 250 nm/min was obtained on the polyimide substrate when the mixture of liquid and vapour precursor was used.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.699-704
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• 2017

Recently, the use of an aluminum nitride(AlN) buffer layer has been actively studied for fabricating a high quality gallium nitride(GaN) template for high efficiency Light Emitting Diode(LED) production. We confirmed that AlN deposition after $N_2$ plasma treatment of the substrate has a positive influence on GaN epitaxial growth. In this study, $N_2$ plasma treatment was performed on a commercial patterned sapphire substrate by RF magnetron sputtering equipment. GaN was grown by metal organic chemical vapor deposition(MOCVD). The surface treated with $N_2$ plasma was analyzed by x-ray photoelectron spectroscopy(XPS) to determine the binding energy. The XPS results indicated the surface was changed from $Al_2O_3$ to AlN and AlON, and we confirmed that the thickness of the pretreated layer was about 1 nm using high resolution transmission electron microscopy(HR-TEM). The AlN buffer layer deposited on the grown pretreated layer had lower crystallinity than the as-treated PSS. Therefore, the surface $N_2$ plasma treatment on PSS resulted in a reduction in the crystallinity of the AlN buffer layer, which can improve the epitaxial growth quality of the GaN template.

• 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 Vacuum Society Conference
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• 2000.02a
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• pp.212-212
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• 2000

Since the first obserbvation of carbon nanotubes, extensive researches have been done for the synthesis using arc discharge, laser vaporization, and plasma-enhanced chemical vapor deposition. Carbon nanotubes have unique physical and chemical properties and can allow nanoscale devices. Vertically aligned carbon nanotubes with high quality on a large area is particularly important to enable both fundamental studies and applications, such as flat panel displays and vacuum microelectronics. we have grown vertically aligned carbon nanotubes on a large area of Si substrates by thermal chemical vapor deposition using C2H2 gas at 750-950$^{\circ}C$. we deposited catalytic metal on Si susbstrate using thermal evaporation. The nanotubes reveal highly purified surface. The carbon nanotubes have multi-wall structure with a hollow inside and it reveals bamboo structure agreed with base growth model. Figure 1 shows SEM micrograph showing vertically aligned carbon nanotubes whih were grown at 950$^{\circ}C$ on a large area (20mm${\times}$30mm) of Si substrates. Figure 2 shows TEM analysis was performed on the carbon nanotubes grown at 950$^{\circ}C$ for 10 min. The carbon nanotubes are multi-wall structure with bamboo shape and the lack of fringes inside the nanotube indicates that the core of the structure is hollow. In our experiment, carbon nanotubes grown by the thermal CVD indicate base growth model.

• Journal of the Korean Vacuum Society
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• v.14 no.4
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• pp.238-244
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• 2005

IZO thin films are prepared on a corning 7059 glass substrate in a mixed gases of Ar +$O_2$ by rf-magnetron sputtering, using a powder target with a composition ratio of $In_{2}O_{3}$ : ZnO=90 : 10 $wt.\%$. Their electrical sheet resistance are strongly dependent on the oxygen concentration introduced during the deposition, a minimum resistivity of $3.7\times10^{-4}\Omega\cdot$ cm and an average transmittance over $85\%$ in the visible range are obtained in a film deposited in pure Ar gas which is close to near the stoichiometry. During the heat treatment from room temperature up tp $600^{\circ}C$ in various environments, the electrical resistance changes are explained by cyrstallizations or oxidizations of In metal and InO contained in the IZO film. The electrical properties due to oxygen adsorption and phase transitions occurring at temperatures over $40000^{\circ}C$ during heat treatment in air are also investigated.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.8 s.185
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• pp.171-177
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• 2006

This study was performed as a part of the research on the development of a maskless and electroless process for fabricating metal micro/nanostructures by using a nanoindenter and an electroless deposition technique. $2-{\mu}m$-deep indentation tests on Ni and Cu samples were performed. The elastic recovery of the Ni and Cu was 9.30% and 9.53% of the maximum penetration depth, respectively. The hardness and the elastic modulus were 1.56 GPa and 120 GPa for Ni and 1.51 GPa and 104 GPa for Cu. The effect of single-point diamond machining conditions such as the Berkovich tip orientation (0, 45, and $90^{\circ}$ ) and the normal load (0.1, 0.3, 0.5, 1, 3, and 5 mN), on both the deformation behavior and the morphology of cutting traces (such as width and depth) was investigated by constant-load scratch tests. The tip orientation had a significant influence on the coefficient of friction, which varied from 0.52-0.66 for Ni and from 0.46- 0.61 for Cu. The crisscross-pattern sample showed that the tip orientation strongly affects the surface quality of the machined are a during scratching. A selective deposition of Cu at the pit-like defect on a p-type Si(111) surface was also investigated. Preferential deposition of the Cu occurred at the surface defect sites of silicon wafers, indicating that those defect sites act as active sites for the deposition reaction. The shape of the Cu-deposited area was almost the same as that of the residual stress field.