콘크리트구조체의 방수용 무기 벤토나이트 분말의 방수성능에 대한 실험적 연구

황은석 漢陽大學校 工學大學院 2004 국내석사

港灣 靜穩度 豫測을 위한 水理模型實驗 및 數値解析技法의 適用

황은석 建國大學校 大學院 1999 국내석사

The hydraulic model test and numerical computation were performed for the prediction of the Nangdo harbor tranquility. The Froude similarity rule was adopted for the construction of the model. The horizontal and vertical scale were taken to be 1/90, consequently giving an undistorted model. The test was performed with unidirectional regular waves for comparing various layouts of harbor protective facilities. The results of the test provided the distribution of wave height inside the harbor. The finite element method was used for the computation of harbor tranquility, using an extended mild slope equation as the governing equation The finite element mesh was organized with the three nodal triangular elements, and the infinite elements were used to treat the radiation condition at infinity. This research will contribute ta the development of the harbor tranquility prediction technique and the reduction of the harbor construction cost, and to the improvement of the cargo handling safety.

Dynamical screening effect by the primordial plasma on the Big Bang nucleosynthesis

황은석 숭실대학교 대학원 2020 국내석사

본 연구는 빅뱅의 핵합성에서 동적 스크리닝 효과에 대하여 논의 한다. 플라즈마 속에서 움직이는 핵은 변형된 쿨롱 퍼텐셜을 갖기때문에 움직이는 핵에는 기존에 잘 알려진 정적 스크리닝 효과와는 다른 동적 스크리닝 효과를 갖는다. 본 연구에서는 동적 스크리닝 효과를 고려하기위해 초기 우주의 플라즈마를 자기화 되지 않은 멕스웰 플라즈마(Maxwellian plasma)로 가정하여 유전율을 계산하고 이를 이용하여 핵반응의 반응률을 구한다. 나아가 동적 스크리닝에 의한 핵반응의 반응률을 빅뱅 핵 합성에 적용하여 원시 핵의 존재비의 변화에 대하여 논의한다. We investigate the dynamic screening effects on big bang nucleosynthesis (BBN). Since the moving ion in plasma causes the distorted Coulomb potential, the screening effect for the dynamic ions is distinct from the usual Salpeter formula. To determine the Coulomb potential of the moving ions in plasma, we calculate the dielectric permittivity considering the varying components from electron-positron-ion to electron-ion plasma during BBN epoch. Assuming the unmagnetized Maxwellian plasma, we obtain the thermal averaged reaction rates for the BBN calculation.

무기성 폐분말 활용 건설재료의 품질특성에 관한 연구

황은석 世明大學校 2019 국내박사

본 연구에서는 무기성 폐분말인 폐콘크리트 미분말 및 폐광산 미분말을 건 설재료로 활용하기 위하여 폐콘크리트 미분말 및 폐광산 미분말의 기초 품질 특성을 평가하였으며, 무기성 폐분말을 활용한 시멘트 경화체 및 흙포장재를 제조하여 품질특성 평가하였다. 무기성 폐분말 활용 시멘트 경화체의 품질특 성을 평가한 결과 폐콘크리트 미분말 및 폐광산 미분말의 혼합율이 증가할수 록 비례적으로 지연되는 경향이 나타났으며, 플로우 및 압축강도의 경우에도 폐콘크리트 미분말 및 폐광산 미분말의 혼합율이 증가할수록 비례적으로 감소 하는 경향이 나타났다. 무기성 폐분말 활용 흙포장재의 품질특성을 평가한 결 과 폐콘크리트 미분말은 혼합하지 않은 경우와 동등수준의 압축강도 확보가 가능한 것으로 나타났으며, 폐광산 미분말은 폐광산 미분말의 충전효과에 의 하여 압축강도가 증가하는 최적 혼합률이 있는 것으로 판단된다. 이상의 결과를 통하여 무기성 폐분말인 폐콘크리트 미분말 및 폐광산 미분 말을 건설재료인 시멘트 경화체와 흙포장재로 활용이 가능할 것으로 판단되 며, 대량의 재활용처가 될 것으로 판단된다. 또한 시멘트계 건설재료와 혼합사 용할 경우 중금속 고정화로 인하여 폐광산 미분말의 환경문제 해소에 기여할 수 있을 것으로 판단된다. 그러나 무기성 폐분말의 혼합율 증가에 따라 품질 성능이 감소하는 특성이 있으므로 소요 성능 확보를 위한 혼화재료 적용 및 배합비 조절 등이 적용 환경에 적합하도록 보정이 필요할 것으로 판단된다. The purpose of this study was to evaluate the basic quality properties of waste concrete powder and waste mine powder, which are inorganic waste powders, in order to use waste concrete powder and waste mine powder as construction materials by manufacturing cement mortar and soil pavement using inorganic waste powders. According to the quality properties of cement mortar made of inorganic waste powders, an increase in the mixture ratio of waste concrete powder and waste mine powder delayed proportional setting time as well as a decrease in flow and compressive strength. According to the quality properties of soil pavement made of inorganic waste powders, waste concrete powder is able to have the same level of compressive strength as that of the not mixed with waste mine powder, - 150 - also waste mine powder has the optimal mixture ratio in which its compressive strength increases due to the filling effect of waste mine powder. Based on the results of our study, waste concrete powder and waste mine powder, which are inorganic waste powders, can be used in cement mortar and soil pavement as construction materials, and be the source of large-scale recycling. Furthermore, when mixed with cement - based construction materials, it can contribute to solving environmental problems of waste mine powder due to immobilization of heavy metals. However, since the quality performance decreases as the mixing ratio of inorganic waste powder increases, it is necessary to calibrate the application of the admixture material and the mixing ratio to ensure the required performance.

InGaZnO based charge trap device for NAND flash memory application

황은석 Seoul National University 2018 국내박사

Current information technology industry requires faster, smaller, less power consuming and cost effective memory devices, which is the fundament of the computer system. Out of many memory devices, NAND flash memory technology one of the promising candidate for next generation storage system. Planar technology is at its roadblocks due to the fundamental limitation of the density per available wafer area. Hence, vertical NAND flash (VNAND) is the solution, which can overcome the density limitation. Current industry use three major types of V-NAND (i.e. BiCs, TCAT and Pipe-BiCs). These major architectures of V-NAND all require “Etch hole”, where ONO, channel and oxide is deposited. Due to limitation on wafer area, etch hole and spacer between etch holes have limitations, often called as the “critical diameter or dimension”. In case of etch hole itself, each packing density has different critical diameter of hole (CD). Currently, a-Si or poly-Si channels are used as the channel material. However, as etch hole depth elongates, to increase cell density, Si based channel suffer from low on current, which can be very problematic in achieving constant device uniformity. To increase on current, Si based channel requires thickening, but again, limited by the CD. Hence, new channel material that can guarantee tunable electrical characteristic is ideal. Out of many candidates, amorphous oxide is one of the promising candidate. InGaZnO (α-IGZO or IGZO) has been well studied to be applied on V-NAND technology. Professor Hosono first proposed IGZO in the year 2004. Since then, IGZO has been intensely studied for its application on display devices. With most common deposition technique, sputtering. Large area, fast deposition rate, and relatively uniform film quality had lead such popularity. In primitive stage of the IGZO research, most problematic characteristic was material’s instability against light illumination under negative bias (NBIS). When light wavelength of 550nm (or shorter) is induced on IGZO (held at negative gate bias), negative shift of the transfer curve was observed. Numerous arguments have been proposed as a possible cause, but most agreed that it was the ionization of the oxygen vacancy. When light is induced, the oxygen vacancy (naturally occurring from amorphous large band gap nature of the material) begins to ionize, changing its valance state from neutron to two (creating two extra electron). Previous research from our group has shown that NBIS is geometry dependent (NBIS worsen as channel length increase), hence, smaller channel dimension may solve the issue. Other possible solutions were to doping and use passivation layer. Despite its intensive study for display application, IGZO’s application on V-NAND still requires major challenge, to change deposition technique. Despite fast and low temperature merits of the sputtering process, its low step coverage hinders IGZO for the memory applications. In this sense, this research proposes relatively new deposition technique to deposit IGZO: metal-organic chemical vapor deposition (MOCVD). First part of this research compares program and erase characteristics of MOCVD and sputter deposited a-IGZO. Both deposition methods have shown to have similar atomic percent (stoichiometry), density and thickness. Despite, slightly higher saturation mobility from sputter IGZO, the program and erase characteristics showed much faster operation in case for the MOCVD IGZO (PGM 3.12V @ VPGM=20V,tPGM=100ms for MOCVD and PGM 1.63V @ VPGM=20V, tPGM=100ms). In depth analysis of such behavior were studied. Second part concerns the composition variation of the IGZO. MOCVD processed IGZO were studied with different Ga/Zn ratio, keeping the In content at constant (40 atomic percent). Previous research has indicated Ga as the carrier sink, allowing the stable off current of the TFT, due to strong bonding between Ga and O. However, study on different Ga/Zn ratio has indicated while highest field effective channel mobility was observed at max Zn content (of the study), highest saturation mobility was observed when Ga/Zn ratio was at maximum (of the study). Analysis to understand the role of Ga/Zn within the IGZO thin film is further investigated