• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.261-262
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• 2006

High temperature superconducting coated conductor has multi-layer structure of protecting layer/superconducting layer/buffer layer/metallic substrate. The buffer layer consists of multi layer, and the architecture most widely used in RABiTS approach is $CeO_2$(cap layer)/YSZ(diffusion barrier layer)/$CeO_2$(seed layer). Multi-buffer layer deposition required many times and process. Therefore single buffer layer deposition study reduce 2G HTS manufacture efforts. Evaporation technique for single buffer deposition method is used for the $CeO_2$ layer. $CeO_2$ single buffer film could be achieved in the chamber. Detailed deposition conditions (temperature and partial gas pressure of deposition) were investigated for the rapid growth of high quality $CeO_2$ single buffer film.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.66-66
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• 2011

Anodic titanium dioxide (TiO2) nanotubes are very attractive materials for gas sensors due to its large surface to volume ratios. The most widely known method for fabrication of TiO2 nanotubes is anodic oxidation of metallic Ti foil. Since the remaining Ti substrate is a metallic conductor, TiO2 nanotube arrays on Ti are not appropriate for gas sensor applications. Detachment of the TiO2 nanotube arrays from the Ti Substrate or the formation of electrodes onto the TiO2 nanotube arrays have been used to demonstrate gas sensors based on TiO2 nanotubes. But the sensitivity was much lower than those of TiO2 gas sensors based on conventional TiO2 nanoparticle films. In this study, Ti thin films were deposited onto a SiO2/Si substrate by electron beam evaporation. Samples were anodized in ethylene glycol solution and ammonium fluoride (NH4F) with 0.1wt%, 0.2wt%, 0.3wt% and potentials ranging from 30 to 60V respectively. After anodization, the samples were annealed at $600^{\circ}C$ in air for 1 hours, leading to porous TiO2 films with TiO2 nanotubes. With changing temperature and CO concentration, gas sensor performance of the TiO2 nanotube gas sensors were measured, demonstrating the potential advantages of the porous TiO2 films for gas sensor applications. The details on the fabrication and gas sensing performance of TiO2 nanotube sensors will be presented.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.52-53
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• 2005

$Y_2O_3$ film was directly deposited on Ni-3at%W substrate using DC reactive sputtering technique. Metallic yttrium was used for DC sputtering target and water vapor was used for oxidizing the deposited metallic Yttrium atoms on the substrate. The window of the water vapor turned out to be broad. The minimum partial pressure of water vapor was determined by sufficient oxidation of the $Y_2O_3$ film, and the maximum partial pressure of water vapor was determined by the non-oxidation of the target surface. As the sputtering power was increased, The deposition rate increased without narrowing the window. The fabricated $Y_2O_3$ films showed good texture qualities and surface morphologies. The YBCO film deposited directly on the $Y_2O_3$ buffered Ni-3at%W substrate showed $T_c$, $I_c$ (77 K, self field), and $J_c$ (77 K, self field) of 89 K, 64 A/cm and 1.l $MA/cm^2$, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.10
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• pp.1011-1017
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• 2012

We report the development of an optical micro-nanolithography method by using a roll-type mask. It includes phase-shift lithography and photolithography for realizing various target dimensions. For sub-wavelength resolution, a structure is achieved using the near-field exposure of a photoresist through a cylindrical phase-mask, allowing high-throughput continuous patterning. By using a film-type metal mask, continuous photolithography was achieved, and this method could be used to control the period of resultant patterns in real time by changing the rotating speed of the cylinder mask. As an application, we present the fabrication of a transparent electrode in the form of a metallic mesh by using the developed roll-type photolithography process. As a result, a transparent conductor with good properties was achieved by using a recently built cylindrical phase-shift lithography prototype, which was designed for patterning on 100-mm2 substrates.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.4
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• pp.658-665
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• 2012

Micro-EDM is widely used in metallic pattern, electronics, nuclear power and industry in the form of precision process. The improvement of Electro Discharge Machining has been on a steady progress since $19^{th}$ century. The technology has overcome the limits of the traditional precision process, enabling micro-EDM, micro electrolytic machining, micro drilling, micro punching and laser beam machining, which create versatile products with smaller sizes. What have been known about the major feature of Micro-EDM is high thermal energy so that their products are free from the hardness of their products as long as they are electrical conductor. However, each metal is suspected to have different features and natures even if they are created through the same procedure. In this thesis, the methodology of Micro-EDM and how to categorize them are explained. Also, the nature of the examined materials with surface shape and surface roughnes are analyzed. The results of the experiments are expected to understand surface roughness and workability of other materials for Micro-EDM.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1075-1076
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• 2006

The wide spread of DC electric railway systems such as urban rapid transits including heavy rail and light rail transits has significant ramification as the stray currents from return conductor rails can cause the electrochemical interference, that is, the electrolytic corrosion of both rails and outside underground metallic infrastructures. The immature understanding of either the railway authority who is responsible for establishing the necessary provisions at the design stage or the affected parties makes it difficult to prepare the optimum range of solutions for the long-pending interference problem. In advanced countries, however, numerous assessment studies have been carried out on the stray current interference, by which protective standards and regulations are provided under the collaboration and agreement of the related parties. In this paper, we introduce a european standard from IEC, namely, "IEC 62128-2:2003 railway applications-fixed installations -part 2: protective provisions against the effects of stray currents caused by d.c. traction systems" and a "Code of Practice" produced by Victorian electrolysis committee (VEC) based on "Electricity Safety Act 1998" and "Electricity safety (stray current corrosion) regulations 1999" of Victoria state, Australia.

• Korean Journal of Materials Research
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• v.15 no.1
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• pp.54-60
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• 2005

Recently a lots of problems have observed in high densified and high integrated electronic components. One of them is ion migration phenomena, which induce the electrical short of electrical circuit. ion migration phenomena has been observed in the field of exposing the specific environment and using for a long tin e. This study was evaluated the generation time of ion migration and was investigated properly test method through water drop test and high temperature high humidity test. Also we observed direct causes and confirmed generation mechanism of dendritic growth as we reproduced the ion migration phenomena. We utilized PCB(printed circuit board) having a comb pattern as follows 0.5, 1.0, 2.0 mm pattern distance. Cu, SnPb and Au were electroplated on the comb pattern. 6.5 V and 15 V were applied in the comb pattern and then we measured the electrical short time causing by ion migration. In these results, we examined a difference of ion migration time depending on pattern materials, applied voltage and pattern spacing of PCB conductor.

• Progress in Superconductivity and Cryogenics
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• v.8 no.4
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• pp.12-14
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• 2006

YBCO coated conductors have been fabricated by the reel-to-reel processing using TFA-MOD method. In this work, the fluorine-free Y & Cu precursor solution was synthesized to shorten the calcining time by reducing the evolution of HF gas, thus the meter-long YBCO precursor films can be made within few hours by the continuous slot-die coating & calcination step using the F-free Y & Cu precursor solution. The annealing step was followed to make the YBCO films by the reel-to-reel method with the vertical gas flow system onto the moving tape. To increase the growth rate of the YBCO films by enhancing the removal of HF gas, the low total pressure was adopted in the annealing processing. And the water partial pressure and the oxygen partial pressure were varied to optimize the growth conditions of the MOD-YBCO films on the buffered metal tape. FE-SEM and XRD were used to investigate the surface morphologies and the texture of the meter-long YBCO films. The end-to-end critical current $(I_c)$ of 63A/cm-width and the critical current density $(J_c)$of $0.9MA/cm^2$ with the thickness of $0.7{\mu}m$ were obtained in the 0.42m long coated conductor.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.3
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• pp.141-147
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• 2019

Recently, the biggest issue in the electricity industry is the increase in renewable energy, and various technologies are being developed to ensure the capacity of the power system. In addition, super-grids linking power systems are being pushed to utilize eco-friendly energy between countries and regions worldwide. The HVDC transmission technology is required to link the power network between regions with different characteristics of the power system such as frequency and voltage. Until now, Korea has applied HVDC transmission technology that connects mainland and Jeju Island with submarine cables. But, the HVDC transmission technology is still developing for long-distance high-capacity power transmission from power parks on the east coast to load-tight areas near the metropolitan area. Considering the high population density and mountainous domestic environment, it is pushing for commercialization of the design technology of the ${\pm}500kV$ Double Bipole with metallic return wire transmission line to transmit large-scale power of 8 GW using minimal right of ways. In this paper, the insulation characteristics were studied for the design of double-bipole transmission tower with metallic return wire, which is the first time in the world. And the air insulation characteristics resistant to the various overvoltage phenomena occurring on transmission lines were verified through a full-scale impulse voltage test.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.9
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• pp.744-750
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• 2013

In this paper, we proposed new type of an artificial magnetic conductor(AMC) structure, which has a high impedance surface for realizing the meta-material characteristics. The designed AMC structure set a goal of 3.2GHz, and the reflector, which consists of periodically arrayed AMCs is fabricated and measured. The high impedance improves the reflection coefficient, decreases the system size and interference, and increases the antenna performance. The structure has embodied the high impedance by the thickness and relative permitivity of the dielectric substrate and the design configuration without the metallic via hole which connects the AMC to the GND. The bandwidth is 150% broader than the similar AMC structures. Also, the distance between the antenna and the AMC reflector is decreased by ${\lambda}/10$ as working as the metal(PEC) reflectors. The antenna radiation characteristics are 3dB increased at 10mm away from reflector by measurement. The proposed reflector could be inserted in the portable mobile devices, and the antenna's performance has improved by the reflector. The specific absorption rate is dramatically decreased over 94% because the back radiation of the antenna is shielded.