• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.7
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• pp.713-717
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• 2004

In this study, the etched trench properties including cross-sectional profile, surface roughness, and crystalline defects were investigated depending on the various silicon etching and additive gases, For the case of HBr$He-O_2SiF_4$ trench etching gas mixtures, the excellent trench profile and minimum defects in the silicon trench were achieved. Due to the residual oxide film grown by the additive oxygen gas, which acts as a protective layer during trench etching, the undercut and defects generation in the trench were suppressed. To improve the electrical characteristics of trench gate, the hydrogen annealing process after trench etching was also adopted. Through the hydrogen annealing, the trench corners might be rounded by the silicon atomic migration at the trench corners having high potential. The rounded trench corner can afford to reduce the gate electric field and grow a uniform gate oxide. As a result, dielectric strength and TDDB characteristics of the hydrogen annealed trench gate oxide were remarkably increased compared to the non-hydrogen annealed one.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.4
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• pp.212-218
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• 2021

In this study, we conducted a design optimization of the Type 4 composite pressure vessels to enhance the pressure-resistant performance of the vessels while keeping the thickness of the composite layer. The design variables for the optimization were the stacking angles of the helical layers of the vessels to improve the performance. Since the carbon fibers are expensive material, it is desirable to reduce the use of the carbon fibers by applying an optimal design of the composite pressure vessel. The structural analysis and optimization process for the design of Type 4 composite pressure vessels were carried out using a commercial finite element analysis software, Abaqus and a plug-in for automated simulation, Isight, respectively. The optimization results confirmed the performance and safety of the optimized Type 4 composite pressure vessels was enhanced by 12.84% compared to the initial design.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.10
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• pp.853-858
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• 2003

In this study, a new simplified technology for fabricating high density trench gate DMOSFETs using only three mask layers and TEOS/nitride spacer is proposed. Due to the reduced masking steps and self-aligned process, this technique can afford to fabricate DMOSFETs with high cell density up to 100 Mcell/inch$^2$ and cost-effective production. The resulting unit cell pitch was 2.3∼2.4${\mu}$m. The fabricated device exhibited a excellent specific on-resistance characteristic of 0.36m$\Omega$. cm$^2$ with a breakdown voltage of 42V. Moreover, time to breakdown of gate oxide was remarkably increased by the hydrogen annealing after trench etching.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.7-11
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• 2022

In the membrane forming process of a proton exchange membrane fuel cell (PEMFC), drying and annealing heat treatment processes are required for performance and durability. In this study, the optimal annealing temperature for improving the durability of the polymer membrane was studied. It was annealed in the temperature range of 125~175 ℃, and thermal stability and hydrogen permeability were measured as basic data of durability at each annealing temperature. The electrochemical durability was analyzed by Fenton reaction and open circuit voltage (OCV) holding. The annealing temperature of 165 ℃ was the optimal temperature in terms of thermal stability and hydrogen permeability. In the Fenton reaction, the fluorine emission rate of the membrane annealed at 165 ℃ was the lowest, and the lifespan of the membrane annealed at 165 ℃ was the longest in the OCV holding experiment, confirming that 165 ℃ was the optimal temperature for the durability of the polymer membrane.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.102-102
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• 2003

• Journal of Magnetics
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• v.13 no.3
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• pp.110-113
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• 2008

In this study, heavy rare earth garnet $Tb_2Bi_1Ga_1Fe_4O_{12}$ powders were fabricated by a sol-gel and vacuum annealing process. The crystal structure was found to be single-phase garnet with a space group of Ia3d. The lattice constant $a_0$ was determined to be 12.465 ${\AA}$. From the analysis of the vibrating sample magnetometer (VSM) hysteresis loop at room temperature, the saturation magnetization and coercivity of the sample are 7.64 emu/g and 229 Oe, respectively. The N$\acute{e}$el temperature($T_N$) was determined to be 525 K. The M$\ddot{o}$ssbauer spectrum of $Tb_2Bi_1Ga_1Fe_4O_{12}$ at room temperature consists of 2 sets of 6 Lorentzians, which is the pattern of single-phase garnet. From the results of the M$\ddot{o}$ssbauer spectrum at room temperature, the absorption area ratios of Fe ions on 24d and 16a sites are 74.7% and 25.3%(approximately 3:1), respectively. These results show that all of the non-magnetic Ga atoms occupy the 16a site by a vacuum annealing process. Absorption area ratios of Fe ions are dependent not only on a sintering condition but also on the temperature of the sample. It can then be interpreted that the Ga ion distribution is dependent on the temperature of the sample. The M$\ddot{o}$ssbauer measurement was carried out in order to investigate the atomic migration in $Tb_2Bi_1Ga_1Fe_4O_{12}$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.165-166
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• 2006

Nb-Ti alloys were hydrogenated to prepare fine and contamination-free powders. Cracks were introduced in the alloys when they were annealed at 1473 K and cooled in a hydrogen atmosphere. The fragments produced by hydrogen-induced cracking are brittle and the friability enhanced with the Ti content of the alloy, which is beneficial for further refinement of particle size. We also demonstrate that Nb-Ti powders with the average particle size less than 1 m can be produced by ball milling at a temperature lower than 203 K. Furthermore, hydrogen-free powders can then be obtained by annealing above the temperature corresponding to hydrogen desorption from Nb solid solution.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.212-216
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• 2021

We investigated the feasibility of hydrogen storage with electrochemically formed VO₂ nanotubes. The VO₂ nanotubes were fabricated through the anodization of vanadium metal in fluoride ion-containing organic electrolyte followed by an annealing process in an Ar-saturated atmosphere at 673 K for 3 h at a heating rate of 3 K /min. During anodization, the current density significantly increased up to 7.93 mA/cm² for approximately 500 s owing to heat generation, which led to a fast-electrochemical etching reaction of the outermost part of the nanotubes. By controlling the anodization temperature, highly ordered VO₂ nanotubes were grown on the metal substrate without using any binders or adhesives. Furthermore, we demonstrated the hydrogen sorption properties of the anodic VO₂ nanotubes.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.29.1-29.1
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• 2009

Fabrication of good quality P-type GaN remained as a challenge for many years which hindered the III-V nitrides from yielding visible light emitting devices. Firstly Amano et al succeeded in obtaining P-type GaN films using Mg doping and post Low Energy Electron Beam Irradiation (LEEBI) treatment. However only few region of the P-GaN was activated by LEEBI treatment. Later Nakamura et al succeeded in producing good quality P-GaN by thermal annealing method in which the as deposited P-GaN samples were annealed in N2 ambient at temperatures above $600^{\circ}C$. The carrier concentration of N type and P-type GaN differs by one order which have a major effect in AlGaN based deep UV-LED fabrication. So increasing the P-type GaN concentration becomes necessary. In this study we have proposed a novel method of activating P-type GaN by electrochemical potentiostatic method. Hydrogen bond in the Mg-H complexes of the P-type GaN is removed by electrochemical reaction using KOH solution as an electrolyte solution. Full structure LED sample grown by MOCVD serves as anode and platinum electrode serves as cathode. Experiments are performed by varying KOH concentration, process time and applied voltage. Secondary Ion Mass Spectroscopy (SIMS) analysis is performed to determine the hydrogen concentration in the P-GaN sample activated by annealing and electrochemical method. Results suggest that the hydrogen concentration is lesser in P-GaN sample activated by electrochemical method than conventional annealing method. The output power of the LED is also enhanced for full structure samples with electrochemical activated P-GaN. Thus we propose an efficient method for P-GaN activation by electrochemical reaction. 30% improvement in light output is obtained by electrochemical activation method.

• Progress in Superconductivity
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• v.14 no.2
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• pp.116-121
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• 2012

Effect of mixed gas and additional Mg powder in an annealing process of the $MgB_2$ is investigated. Four different type of samples were prepared, each in different annealing environment of Ar, $Ar+4%H_2$, Ar with Mg powder and $Ar+4%H_2$ with Mg powder. Different annealing environment did not affect the electron-phonon interaction which is reflected from the same superconducting transition of 36.6 K for all samples. The reducing effect of hydrogen is clearly depicted from the presence of excess Mg in sample synthesized in $Ar+4%H_2$ gas implying the reduced rate of reaction between Mg and B. This has manifested itself in terms of slightly increased high-field critical current density of the sample. In contrast, the sample synthesized in $Ar+4%H_2$ with Mg powder, has shown overall enhancement in the superconducting properties as presented by higher diamagnetic saturation and critical current density.