• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.5-5
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• 2009

Thin-film-transistors (TFTs) that can be prepared at low temperatures have attracted much attention because of the great potential for transparent and flexible electronics. One of the mainstreams in this field is the use of organic semiconductors such as pentacene. But device performance of the organic TFTs is still limited due to low field-effect mobility and rapid degradation after exposing to air. Alternative approach is the use of amorphous oxide semiconductors as a channel. Amorphous oxide semiconductors (AOSs) based TFTs showed the fast technological development, because AOS films can be fabricated at room temperature and exhibit the possibility in application like flexible display, electronic paper, and larges solar cells. Among the various AOSs, a-IGZO has lots of advantages because it has high channel mobility, uniform surface roughness and good transparency. [1] The high mobility is attributed to the overlap of spherical s-orbital of the heavy post-transition metal cations. This study demonstrated the effect of the variation in channel thickness from 30nm to 200nm on the TFT device performance. When the thickness was increased, turn-on voltage and subthreshold swing was decreased. The a-IGZO channels and source/drain metals were deposited with shadow mask. The a-IGZO channel layer was deposited on $SiO_2$/p-Si substrates by RF magnetron sputtering, where RF power is 150W. And working pressure is 3m Torr, at $O_2/Ar$ (2/28 sccm) atmosphere. The electrodes were formed with electron-beam evaporated Ti (30 nm) and Au (70 nm) bilayer. Finally, Al (150nm) as a gate metal was thermal-evaporated. TFT devices were heat-treated in a furnace at 250 $^{\circ}C$ and nitrogen atmosphere for 1hour. The electrical properties of the TFTs were measured using a probe-station. The TFT with channel thickness of 150nm exhibits a good subthreshold swing (SS) of 0.72 V/decade and on-off ratio of $1{\times}10^8$. The field effect mobility and threshold voltage were evaluated as 7.2 and 8 V, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.107-112
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• 1999

The ZnSe/GaAs epilayers were grown by RF reactive sputtering. In order to obtain the optimum condition of the growth, we have studied the dependence of Ar pressure, input power of sputter, temperature of substrate, and the distande between substrate and target. Through the observation of the grown epilayer via electronic microscope, we confirmed that the layer's surface was uniform and the boundary of the substrate and the layer was well defined. The defotmation of lattice distortion and the distortion ratio were obtained by DCRC measurements. From mrasurements of photoluminescence, in the ZnSe/GaAs sample without injection of $N_2$gas, we found that the intensity of bound exciton $I_2$is stronger than that of $I_1$and the bound exiton $I_1$represents the deep acceptor level, $I_1\;^d$. On the other hand, in the ZnSe/GaAs sample with injection of$N_2$gas, the peak of$I_1$ was much higher than that of the $I_2$and the half width appeared to be narrow. We concluded that the p-type of ZnSe/GaAs epilayer was grown successfully, because of stronger peak of the bound exciton $I_1$due to the $N_2$dopping.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.249-249
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• 2009

We have grown large area BSTO($(Ba_{1-x}Sr_x)TiO_3$) thin films (x=0.4) on 2 inch diameter MgO (001) single crystal substrates using a pulse laser deposition(PLD) system. Substrate temperature and oxygen pressure in the deposition chamber, and the laser optics for ablating a target have been controlled to obtain the uniform thickness and preferred orientation of the films. Results of x-ray diffraction and rocking curve analysis revealed that the BSTO films were grown on MgO substrates with a preferred orientation (002), and the full width half maximum of the rocking curve was measured to be 0.86 degree at optimum condition. Roughness of the films have been measured to be $3.42{\AA}$ rms by using atomic force microscopy. We have successfully deposited the large area BSTO thin films of $4000{\AA}$ thickness on 50 mm diameter MgO substrates.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.4
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• pp.103-112
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• 1991

In this study, a numerical model was established and applied to simulate the steady-state groundwater and heat flow in an isotropic, heterogeneous, three dimensional aquifer system with uniform thermal properties and no change of state. This model was developed as an aid in screening large groundwater-flow systems as prospects for underground waste storage. Driving forces on the system are external hydrologic conditions of recharge from precipitation and fixed hydraulic head boundaries. Heat flux includes geothermal heat-flow, conduction to the land surface, advection from recharge, and advection to or from fixed-head boundaries. The model uses an iterative procedure that alternately solves the groundwater-flow and heat-flow equations, updating advective flux after solution of the groundwater-flow equation, and updating hydraulic conductivity after solution of the heat-flow equation. Dierect solution is used for each equation. Travel time is determined by particle tracking through the modeled space. Velocities within blocks are linear interpolations of velocities at block faces. Applying this model to the groundwater-flow system located in Jigyung-ri. Songla-myun, Youngil-gun. Kyungsangbuk-do, the groundwater-flow system including distribution of head, temperature and travel time and flow line, is analyzed.

• Composites Research
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• v.33 no.5
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• pp.315-320
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• 2020

In this study, when strand specimens were manufactured using an automatic winding device to obtain uniform strand specimens, analysis and test were conducted to investigate the effect of thermal expansion of the mandrel on strand specimens. Also, necessity of changing materials and mandrel configuration was checked. According to the results, strand specimen received unintended tension that was created by thermal expansion of the mandrel and this unintended tension depended on the curing temperature and position of specimens. Tensile test was conducted to check that initial tension affected on the performance of carbon fiber tow prepreg. All other conditions were fixed and only the initial tension was controlled at 40 N, 60 N, and 80 N. From the results of analysis and test, neither additional tension and tension deviation due to the thermal expansion of the mandrel and the initial tension difference had a significant effect on tensile test results, because carbon fiber had sufficiently high strength compared with tension. Therefore, it was confirmed that the change of the mandrel material and configuration of the automatic winding device was unnecessary.

• Applied Chemistry for Engineering
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• v.20 no.4
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• pp.381-385
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• 2009

A basic objective is the preparation and surface studies of supported molten salt catalysts because molten salts can stay as the liquid phase in the range of the ordinary reaction temperature. Many kinds of metal salt mixtures for the formation of molten salt phase are appliable but CuCl and KCl were selected in this study because Cu is considered catalytically reactive in many reactons. The loading of the molten salt was selected as 25 vol% of the total pore volume of ${\gamma}-alumina$ to provide reasonable exposed surface area. The surface structure of catalysts containing molten salts in the ${\gamma}-alumina$ was studied using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). CuCl and KCl were added into the ${\gamma}-alumina$ using concentrated hydrochloric acid solution by the impregnation technique. The surfaces of the prepared catalysts before and after heat treatments were compared and they suggested that the heat treatment of catalysts helped the formation of molten-salt although the surface compositions of CuCl and KCl were not uniform.

• Korean Journal of Materials Research
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• v.10 no.3
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• pp.204-211
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• 2000

The $(Y,Gd)BO_3:Eu$ red phosphors for PDP application were synthesized by ultrasonic spray method and then their photoluminance properties were investigated under 147nm VUV irradiation. The precursor solution of acetates of Y, GD and Eu and boric acid diluted in water was sprayed using 1.7 MHz ultra-sonic sprayer into the reaction tube held at high temperature. The as-sprayed particles were amorphous phase having C-C and C-H bonds due to the insufficient thermal reaction during the pass along the tube. But the sprayed samples followed by heat treatment at $1100^{\circ}C$ had the same crystal structure and chemical composition as those samples followed by solid state reaction. It was found that the $(Y_{0.7}Gd_{0.3})_{0.95} BO_3:Eu_{0.05}^{3+}$ phosphor particles synthesized by spray at $500^{\circ}C$ and then heat treated at $900^{\circ}C$ had a spherical-like shape and fine particle size at $0.7{\mu\textrm{m}}$ having a narrow size distribution, while the phosphor particles made by solid state reaction was $3{\mu\textrm{m}}$ coarse and non-uniform size distribution. The emitting intensity under 147nm VUV excitation for $(Y_{0.7}Gd_{0.3})_{0.95}BO_3:Eu_{0.05}^{3+}$ phosphor prepared by spray method was found to be higher than those phosphor made by solid state reaction and the commercial $(Y,Gd)BO_3:Eu$ product.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.4
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• pp.679-686
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• 1997

In order to investigate the distribution characteristics of polychlorinated Biphenyls (PCBs) at the southern of Korean East Sea, vertical measurements of temperature, salinity, DO and PCBs were performed by each depth of 5 stations during August - October 1996. Thermocline and salinocline were generally existed at depth of 30 m and water mass current of midwater in the southern of Korean East Sea was distributed below 30 m depth. The distribution of surface water mass in this area was extended to Tsusima area from the southern offshore of the Korean last Sea. In August 1996, concentration range of PCBs had $0.22\~0.36\;ng/\ell$ at surface layer and their concentrations at near Tsusima offshore were relatively decreased. Total mean concentration of PCBs was $0.29\;ng/\ell$ in the sea surface and $0.31\;ng/\ell$ in the middle layer. PCBs seemed to correlate well with suspended particles. And vortical and horizontal distribution of their concentrations showed comparatively uniform pattern. Relatively high compositional ratio of Di- and Tri-PCBs could be found at the sea surface, while compositional ratio of Penta-PCBs dominates over other congener at deep layer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.6
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• pp.1274-1279
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• 2011

The purpose of this paper is to present the manufacturing defect and damage pattern of a 3 phase 22.9/3.3kV oil immersed transformer, as well as to present an objective basis for the prevention of a similar accident and to secure data for the settlement of PL related disputes. It was found that in order to prevent the occurrence of accidents to transformers, insulating oil analysis, thermal image measurement, and corona discharge diagnosis, etc., were performed by establishing relevant regulation. The result of analysis performed on the external appearance of a transformer to which an accident occurred, the internal insulation resistance and protection system, etc., showed that most of the analysis items were judged to be acceptable. However, it was found that the insulation characteristics between the primary winding and the enclosure, those between the ground and the secondary winding, and those between the primary and secondary windings were inappropriate due to an insulating oil leak caused by damage to the pressure relief valve. From the analysis of the acidity values measured over the past 5 years, it is thought that an increase in carbon dioxide (CO2) caused an increase in the temperature inside the transformer and the increase in the ethylene gas increased the possibility of ignition. Even though 17 years have passed since the transformer was installed, it was found that the system's design, manufacture, maintenance and management have been performed well and the insulating paper was in good condition, and that there was no trace of public access or vandalism. However, in the case of transformers to which accidents have occurred, a melted area between the upper and the intermediate bobbins of the W-phase secondary winding as well as between its intermediate and lower bobbins. It can be seen that a V-pattern was formed at the carbonized area of the transformer and that the depth of the carbonization is deeper at the upper side than the lower side. In addition, it was found that physical bending and deformation occurred inside the secondary winding due to non-uniform pressure while performing transformer winding work. Therefore, since it is obvious that the accident occurred due to a manufacturing defect (winding work defect), it is thought that the manufacturer of the transformer is responsible for the accident and that it is lawful for the manufacture to investigate and prove the concrete cause of the accident according to the Product Liability Law (PLL).

• The KIPS Transactions:PartA
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• v.15A no.3
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• pp.141-149
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• 2008

In this research we present a novel method which combines and visualizes the design model and the FDM-based simulation result of solidification. Moreover we employ VR displays and visualize stereoscopic images to provide an effective analysis environment. First we reconstruct the solidification simulation result to a rectangular mesh model using a conventional simulation software. Then each point color of the reconstructed model represents a temperature value of its position. Next we map the two models by finding the nearest point of the reconstructed model for each point of the design model and then assign the point color of the design model as that of the reconstructed model. Before this mapping we apply mesh subdivision because the design model is composed of minimum number of points and that makes the point distribution of the design model not uniform compared with the reconstructed model. In this process the original shape is preserved in the manner that points are added to the mesh edge which length is longer than a predefined threshold value. The implemented system visualizes the solidification simulation data on the design model, which allows the user to understand the object geometry precisely. The immersive and realistic working environment constructed with use of VR display can support the user to discover the defect occurrence faster and more effectively.