• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.290-294
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• 2010

We performed a density functional theory study to investigate the intercalation voltage and lithium ion conduction in lithium cobalt oxide for lithium ion battery as a function of the lithium concentration. There were two methods for the intercalation of lithium ions; the intercalation of a lithium ion at a time in the individual layer and the intercalation of lithium ions in all the sites of one layer after all the sites of another layer. The average intercalation voltage was the same value, 3.48 V. However, we found the former method was more favorable than the latter method. The lattice parameter c was increased as the increase of the lithium concentration in the range of x < 0.25 while it was decreased as increase of the lithium concentration in the range of x > 0.25. The energy barrier for the conduction of lithium ion in lithium cobalt oxide was increased as the lithium concentration was increased. We demonstrated that the decrease of the intercalation voltage and increase of the energy barrier as the increase of the lithium concentration caused lower output voltage during the discharge of the lithium ion battery.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.246-252
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• 2016

In this paper, reduction of monostatic RCS by DBD plasma is measured. For the calibration of monostatic RCS, S-parameters of two metallic plate in different sizes are used and the result is within 0.4 dB error. Metallic plate is put behind DBD plasma generator for measuring reduction of monostatic RCS by DBD plasma. To prevent arc discharge between metallic plate and DBD plasma generator, measurement is progressed spacing the interval between metallic plate and DBD plasma generator. As a result, maximum reduction of monostatic RCS is about 3 dB at 7.4 GHz.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.102-102
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• 2018

Electronic industry had required the finer size and the higher performance of the device. Therefore, 3-D die stacking technology such as TSV (through silicon via) and micro-bump had been used. Moreover, by the development of the 3-D die stacking technology, 3-D structure such as chip to chip (c2c) and chip to wafer (c2w) had become practicable. These technologies led to the appearance of HBM (high bandwidth memory). HBM was type of the memory, which is composed of several stacked layers of the memory chips. Each memory chips were connected by TSV and micro-bump. Thus, HBM had lower RC delay and higher performance of data processing than the conventional memory. Moreover, due to the development of the IT industry such as, AI (artificial intelligence), IOT (internet of things), and VR (virtual reality), the lower pitch size and the higher density were required to micro-electronics. Particularly, to obtain the fine pitch, some of the method such as copper pillar, nickel diffusion barrier, and tin-silver or tin-silver-copper based bump had been utillized. TCB (thermal compression bonding) and reflow process (thermal aging) were conventional method to bond between tin-silver or tin-silver-copper caps in the temperature range of 200 to 300 degrees. However, because of tin overflow which caused by higher operating temperature than melting point of Tin ($232^{\circ}C$), there would be the danger of bump bridge failure in fine-pitch bonding. Furthermore, regulating the phase of IMC (intermetallic compound) which was located between nickel diffusion barrier and bump, had a lot of problems. For example, an excess of kirkendall void which provides site of brittle fracture occurs at IMC layer after reflow process. The essential solution to reduce the difficulty of bump bonding process is copper to copper direct bonding below $300^{\circ}C$. In this study, in order to improve the problem of bump bonding process, copper to copper direct bonding was performed below $300^{\circ}C$. The driving force of bonding was the self-annealing properties of electrodeposited Cu with high defect density. The self-annealing property originated in high defect density and non-equilibrium grain boundaries at the triple junction. The electrodeposited Cu at high current density and low bath temperature was fabricated by electroplating on copper deposited silicon wafer. The copper-copper bonding experiments was conducted using thermal pressing machine. The condition of investigation such as thermal parameter and pressure parameter were varied to acquire proper bonded specimens. The bonded interface was characterized by SEM (scanning electron microscope) and OM (optical microscope). The density of grain boundary and defects were examined by TEM (transmission electron microscopy).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.2
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• pp.123-131
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• 2021

The buffer is a key component of an engineered barrier system that safeguards the disposal of high-level radioactive waste. Buffers are located between disposal canisters and host rock, and they can restrain the release of radionuclides and protect canisters from the inflow of ground water. Since considerable heat is released from a disposal canister to the surrounding buffer, the thermal conductivity of the buffer is a very important parameter in the entire disposal safety. For this reason, a lot of research has been conducted on thermal conductivity prediction models that consider various factors. In this study, the thermal conductivity of a buffer is estimated using the machine learning methods of: linear regression, decision tree, support vector machine (SVM), ensemble, Gaussian process regression (GPR), neural network, deep belief network, and genetic programming. In the results, the machine learning methods such as ensemble, genetic programming, SVM with cubic parameter, and GPR showed better performance compared with the regression model, with the ensemble with XGBoost and Gaussian process regression models showing best performance.

• Composites Research
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• v.30 no.2
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• pp.84-93
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• 2017

This study investigates thermal and mechanical characterization of environmental barrier coating on the $SiC_f-SiC$ composites. The spherical environmental barrier coating (EBC) powders are prepared using a spray drying process for flowing easily during coating process. The powders consisting of mullite and 12 wt% of Ytterbium silicate are air plasma sprayed on the Si bondcoat on the LSI SiC fiber reinforced SiC composite substrate for protecting the composites from oxidation and water vapor reaction. We vary the process parameter of spray distance during air plasma spray of powders, 100, 120 and 140 mm. After that, we performed the thermal durability tests by thermal annealing test at $1100^{\circ}C$ for 100hr and thermal shock test from $1200^{\circ}C$ for 3000 cycles. As a result, the interface delamination of EBC never occur during thermal durability tests while stable cracks are prominent on the coating layer. The crack density and crack length depend on the spray distance during coating. The post indentation test indicates thermal tests influence on the indentation load-displacement mechanical behavior.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.134-134
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• 2011

High-k dielectric materials such as $HfO_2$, $ZrO_2$ and $Al_2O_3$ increase gate capacitance and reduce gate leakage current in MOSFET structures. This behavior suggests that high-k materials will be promise candidates to substitute as a tunnel barrier. Furthermore, stack structure of low-k and high-k tunnel barrier named variable oxide thickness (VARIOT) is more efficient.[1] In this study, we fabricated the $WSi_2$ nanocrystals nonvolatile memory device with $SiO_2/HfO_2/Al_2O_3$ tunnel layer. The $WSi_2$ nano-floating gate capacitors were fabricated on p-type Si (100) wafers. After wafer cleaning, the phosphorus in-situ doped poly-Si layer with a thickness of 100 nm was deposited on isolated active region to confine source and drain. Then, on the gate region defined by using reactive ion etching, the barrier engineered multi-stack tunnel layers of $SiO_2/HfO_2/Al_2O_3$ (2 nm/1 nm/3 nm) were deposited the gate region on Si substrate by using atomic layer deposition. To fabricate $WSi_2$ nanocrystals, the ultrathin $WSi_2$ film with a thickness of 3-4 nm was deposited on the multi-stack tunnel layer by using direct current magnetron sputtering system [2]. Subsequently, the first post annealing process was carried out at $900^{\circ}C$ for 1 min by using rapid thermal annealing system in nitrogen gas ambient. The 15-nm-thick $SiO_2$ control layer was deposited by using ultra-high vacuum magnetron sputtering. For $SiO_2$ layer density, the second post annealing process was carried out at $900^{\circ}C$ for 30 seconds by using rapid thermal annealing system in nitrogen gas ambient. The aluminum gate electrodes of 200-nm thickness were formed by thermal evaporation. The electrical properties of devices were measured by using a HP 4156A precision semiconductor parameter analyzer with HP 41501A pulse generator, an Agillent 81104A 80MHz pulse/pattern generator and an Agillent E5250A low leakage switch mainframe. We will discuss the electrical properties for application next generation non-volatile memory device.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.4
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• pp.121-133
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• 2015

The TANK model has been widely used in rainfall-runoff modeling due to its simplicity of concept and computation while achieving forecast accuracy. A major barrier to the model application is to determine parameter values for ungauged watersheds, leading to the need of a method for the parameter estimation. The objective of this study was to develop regression equations for estimating the 3th TANK model parameters considering their variations for the ungauged watersheds. Thirty watersheds of dam sites and stream stations were selected for this study. A genetic algorithm was used to optimize TANK model parameters. Watershed characteristics used in this study include land use percent, watershed area, watershed length, and watershed average slope. Generalized equations were derived by correlating to the optimized parameters and the watershed characteristics. The results showed that the TANK model, with the parameters determined by the developed regression equations, performed reasonably with 0.60 to 0.85 of Nash-Sutcliffe efficiency for daily runoff. The developed regression equations for the TANK model can be applied for the runoff simulation particularly for the ungauged watersheds, which is common for upstream of agricultural reservoirs in Korea.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.150-150
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• 2008

본 연구에서는 Wet chemistry damage가 Nanopatterned p-ohmic electrode에 미치는 영향을 연구하였다. Nanopattern은 Metal clustering을 이용하여, P-GaN와 Ohmic형성에 유리한 Pd을 50$\AA$ 적층한 후 Rapid Thermal Annealing방법으로 $850^{\circ}C$, $N_2$분위기에서 3min열처리를 하여 Pd Clustering mask 를 제작하였다. Wet etching은 $85^{\circ}C$, $H_3PO_4$조건에서 시간에 따라 Sample을 Dipping하는 방법으로 시행하였다 Ohmic test를 위해서 Circular - Transmission line Model 방법을 이용하였으며, Atomic Force Microscopy과 Parameter Analyzer로 Nanopatterned GaN surface위에 형성된 Ni/ Au Contact에서의 전기적 분석과, 표면구조분석을 시행하였다. AFM결과 Wet처리시간에 따라서 Etching형상 및 Etch rate이 영향을 받는 것이 확인되었고, Ohmic test에서 Wet chemistry처리에 의한 Tunneling parameter와 Schottky Barrier Height가 크게 증/감함을 관찰하였다. 이러한 결과들은 Wet처리에 의해서 발생된 Defect가 GaN의 표면과 하부에서 발생되며, Deep acceptor trap 및 transfer거동과 밀접한 관련이 있음을 확인 할 수 있었다. 보다 자세한 Transport 및 Wet chemical처리영향에 관한 형성 Mechanism은 후에 I-V-T, I-V, C-V, AFM결과 들을 활용하여 발표할 예정이다.

• Journal of Radiation Protection and Research
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• v.16 no.1
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• pp.53-72
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• 1991

An integrated model is developed in this paper for the performance assessment of high level radioactive waste repository. This integrated model consists of two simple mathematical models. One is a multiple-barrier failure model of the repository system based on constant failure rates which provides source terms to biosphere. The other is a biosphere model which has multiple pathways for radionuclides to reach to human. For the parametric uncertainty and sensitivity analysis for the risk assessment of high level radioactive waste repository, Latin hypercube sampling and rank correlation techniques are applied to this model. The former is cost-effective for large computer programs because it gives smaller error in estimating output distribution even with smaller number of runs compared to crude Monte Carlo technique. The latter is good for generating dependence structure among samples of input parameters. It is also used to find out the most sensitive, or important, parameter groups among given input parameters. The methodology of the mathematical modelling with statistical analysis will provide useful insights to the decision-making of radioactive waste repository selection and future researches related to uncertain and sensitive input parameters.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.5
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• pp.552-558
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• 2013

In recent years the interest on flexible display has been increasing as a future display due to its bendable characteristics. An ITO(indium tin oxide) layer, which is part of a flexible display, can be broken easily while bending because it is made of brittle materials. This brittle property can cause the malfunction of flexible display. To analyze fracture characteristics of ITO layer, bending test was conducted commonly. However, it is not possible to know specific phenomena on bended ITO layer by simple bending test only. Accordingly, in this study, the FE(finite element) model is developed similarly to a real flexible display to analyze stress distribution of flexible display under bending condition, especially on ITO layer. To validate FE model, actual bending test was conducted and the test results were compared with the simulation results by measuring reaction forces during bending. By using the developed model, FE analysis about the effect of design parameter (Thickness & Young's Modulus of BL) on ITO Layer was performed. By explained FE analysis above, this research draws a conclusion of reliable design guide of flexible display, especially on ITO layer.