• 한국생산제조학회지
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• 제25권2호
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• pp.124-131
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• 2016

Several research works for finding and optimizing the methods of dispensing high viscosity phosphor used in the fabrication of white LED's are currently in progress. High viscosity phosphor dispensing with a high accuracy is crucial because the dispensing rate and uniformity directly affect parameters such as the CIE chromaticity diagram, color temperature and luminous flux of white LED's. This study presents a novel method of dispensing high viscosity phosphor using electrohydrodynamic printing. The dispensing rate was optimized less than 0.01 mg phosphor using experiments and optimizing the process parameters including the standoff distance from the nozzle to the substrate, ink supply pressure, and multi-step pulsed waveform magnitude ratio. The dispensing rate was measured by dispensing 20 dots using drop-on-demand with the optimized parameters, and the experiments were repeated 10 times to maximize the data accuracy. The average dispensing rate that can be reliably used for high viscosity phosphor dispensing was 0.0052 mg.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.110-112
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• 2006

Membrane electrode assembly (MEA) for polymer electrolyte fuel cell (PEFC) are commonly prepared in the research laboratory by spraying, screen-printing and brushing catalyst slurry onto membrane or other support material like carbon paper or polyimide film in a batch style. These hand applications of the catalyst slurry are painstaking process with respect to precision of catalyst loading and reproducibility. It has been generally mentioned that the adoption of continuous process is very helpful to develop the reliable product. In the present work, we report the results of using continuous type coater with doctor-blade to coat catalyst slurry for preparing the MEA catalyst layers In a faster and highly reproducible fashion. We show that while expectedly faster than batch style, the machine coater requires the use of slurry of appropriate composition and a properly selected transfer decal material in order to achieve superior MEA plat lnw loading reproducibility. To make highly viscous catalyst slurry that is imperative for using coater, we use 40wt.% Nafion solution and minimize the content of organic solvent. And the choice of proper high surface area catalyst is important in the viewpoint of making well-dispersed slurry. After catalyst coating onto the support material, we transferred the catalyst layer to both sides of Nafion membrane by hot-pressing In this case, the degree of transfer was Influenced by hot-pressing condition including temperature, pressure, and time. To compare the transferring ability, we compared so many films and detaching papers. And among the support, polyethylene terephthalate(PET) film shows the prominent result.

• 전기전자학회논문지
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• 제26권2호
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• pp.205-210
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• 2022

본 연구에서는 유기 발광 다이오드(OLED)의 광추출 향상을 위한 롤투롤 마이크로컨택(mCP)방식으로 인쇄된 마이크로렌즈 어레이(MLA)를 제시하였다. 상업적으로 사용되는 마이크로렌즈 어레이를 템플레이트로 사용하여서 polydimethylpolysiloxane(PDMS)를 롤스탬프로 제작하였다. 낮은 끓는 점을 가지는 불소화 잉크로부터 PDMS 롤스탬프에 고분자 박막을 형성하고 이를 OLED의 하부면에 고압·고온 처리 없이 인쇄하였다. 최적화된 농도를 찾아서 템플레이트로 사용된 MLA와 거의 동일한 모양의 패턴을 성공적으로 인쇄하였다. 마이크로컨택 방식으로 인쇄된 MLA의 구조와 소재의 낮은 흡수도로 인해서 OLED의 외부양자효율이 18% 향상되었다.

• Tribology and Lubricants
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• 제38권5호
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• pp.199-204
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• 2022

This paper presents a numerical investigation of the influence of water molecule thickness on frictional behavior at the nanoscale using molecular dynamics simulation. Three different models, comprising water thin films of various thicknesses, were built, and indentation and sliding simulations were performed using the models. Various normal loads were applied by indenting the Si tip on the water film for the sliding simulation to evaluate the interplay between the water thin film thickness and the normal load. The results of the simulations showed that the friction force generally increased with respect to the normal load and thickness of the water thin film. The friction coefficient varied with respect to the normal load and the water film thickness. The friction coefficient was the smallest under a moderate normal force and increased with decreasing or increasing normal loads. As the water film became thicker, the contact area between the tip and water film became larger. Under well-lubricated conditions, the friction force was proportional to the contact area regardless of the water film thickness. As the normal force increased above a critical condition, the water molecules beneath the Si tip spread out; thus, the film could not provide lubrication. Consequently, the substrate was permanently deformed by direct contact with the Si tip, while the friction force and friction coefficient significantly increased. The results suggest that a thin water film can effectively reduce friction under relatively low normal load and contact pressure conditions. In addition, the contact area between the contacting surfaces dominates the friction force.

• 전자통신동향분석
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• 제38권6호
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• pp.41-51
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• 2023

Heat dissipation technology for semiconductors and electronic packaging has a substantial impact on performance and lifespan, but efficient heat dissipation is currently facing limited improvement. Owing to the high integration density in electronic packaging, heat dissipation components must become thinner and increase their performance. Therefore, heat dissipation materials are being devised considering conductive heat transfer, carbon-based directional thermal conductivity improvements, functional heat dissipation composite materials with added fillers, and liquid-metal thermal interface materials. Additionally, in heat dissipation structure design, 3D printing-based complex heat dissipation fins, packages that expand the heat dissipation area, chip embedded structures that minimize contact thermal resistance, differential scanning calorimetry structures, and through-silicon-via technologies and their replacement technologies are being actively developed. Regarding dry cooling using single-phase and phase-change heat transfer, technologies for improving the vapor chamber performance and structural diversification are being investigated along with the miniaturization of heat pipes and high-performance capillary wicks. Meanwhile, in wet cooling with high heat flux, technologies for designing and manufacturing miniaturized flow paths, heat dissipating materials within flow paths, increasing heat dissipation area, and reducing pressure drops are being developed. We also analyze the development of direct cooling and immersion cooling technologies, which are gradually expanding to achieve near-junction cooling.

• 공업화학
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• 제34권5호
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• pp.493-500
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• 2023

본 연구에서는 스크린 프린팅 공정을 통해 탄소 잉크 기반의 2상 전극을 제작하고, 전극 표면에 이리듐 산화물(IrO_x)을 코팅함으로써 전극의 분극 현상을 제어할 수 있는 임피던스 센서를 개발하였다. IrO_x는 순환 전압 전류법으로 탄소 전극의 표면 위에 순환 수(0~50 cycles)에 따라서 코팅되었다. 전자주사현미경을 이용하여 cycle 수가 증가할수록 IrO_x 입자의 크기와 수가 증가하는 경향성을 확인하였다. 전기화학 임피던스 분석을 이용하여 상기 제조된 센서들의 NaCl 농도에 따른 임피던스 변화 값을 조사하였다. 50 cycle에서 제조된 센서가 가장 우수한 결정계수와 재현성을 나타내었으며, 이는 분극 현상이 잘 제어되었기 때문이다. 실제 용액 샘플들을 이용한 삼투압 장비와 비교 측정 실험을 수행함으로써 IrO_x 기반 센서의 안구건조증 진단 센서로의 활용가치를 증명하였다.

• 대한심미치과학회지
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• 제30권2호
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• pp.71-90
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• 2021

가상 환자 데이터 세트는 단일 환자로부터 획득한 구강스캔 안면스캔 전신스캔 하악운동경로데이터 등 다양한 소스의 진단 데이터를 하나의 3차원 좌표계로 정렬한 데이터의 집합이다. 치과의사는 가상 환자 데이터 세트를 사용하여 효과적으로 치료 계획을 수립하고 다양한 치료 계획을 가상공간상에서 시뮬레이션 할 수 있으며, 가상 환자 데이터 세트에서 환자의 미소를 디자인 후 그 결과를 시뮬레이션하고 최적의 치료결과를 선택할 수 있다. 가상공간에서 선택된 치료 계획은 3D 프린팅, 밀링, 사출 성형과 같은 제조 기술을 사용하여 환자에게 동일하게 전달될 수 있다. 이러 치료 계획의 전달은 임시 수복물 제작 및 환자의 구강 내에서 목업 확인을 통해 최종 보철물 제작으로 연결할 수 있다. 이와 같이 진단 데이터, 중첩 및 가공의 정확도가 보장된다면 3차원 가상공간 상에서 시뮬레이션된 3D 디지털 스마일 디자인을 실제 환자에게 정확하게 전달할 수 있다. 가상환자데이터세트의 임상적용방법으로 동기능적교합측정 검사를 통해 교합조정치료를 치료계획에서 배제할수 있는 의사결정방법과, 턱관절질환을 가지고 있는 청소년기 특발성 척추측만증 환자의 턱관절 치료전후 전신스캔 비교분석방법, 그리고 전악수복증례인 상하악 총의치환자 진료시 가상환자데이터세트에 기반한 교합평면분석 및 디지털심미분석방법을 제시하였다.

• 동력기계공학회지
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• 제20권4호
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• pp.75-82
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• 2016

In this paper, we developed a 3D printing system using a photo-curing resin in order to reduce the surface roughness of a sculpture produced with the 3D printer. Using the pattern of the resulting variable thickness, that gave rise to a stepped shape, and the area error of the photo-curable sculpture, a study was carried out for the process to reduce the surface roughness. At a given value of stage velocity (40~70 mm/s) and output air pneumatic pressure (20~60 kPa), the minimum pattern thickness of the pattern was achieved $65{\mu}m$ and the maximum pattern thickness of up to $175{\mu}m$. To increases the pattern resolution to about $40{\mu}m$, the process conditions should be optimized. 3D surface Nano profiler was used to find the surface roughness of the sculpture that was measured to be minimum $4.7{\mu}m$ and maximum $8.7{\mu}m$. The maximum surface roughness was reduced about $1.2{\mu}m$ for the maximum thickness of the pattern. In addition, a FDM was used to fabricate the same sculpture and its surface roughness measurements were also taken for comparison with the one fabricated using photo-curing. Same process conditions were used for both fabrication setups in order to perform the comparison efficiently. The surface roughness of the photo-curable sculpture is $5.5{\mu}m$ lower than the sculpture fabricated using FDM. A certain circuit patterns was formed on the laminated surface of the photo-curable sculpture while there was no stable pattern on the laminated surface of the FDM based sculpture the other hand.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.344-344
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• 2014

Transparent amorphous oxide semiconductors such as a In-Ga-Zn-O (a-IGZO) have advantages for large area electronic devices; e.g., uniform deposition at a large area, optical transparency, a smooth surface, and large electron mobility >10 cm2/Vs, which is more than an order of magnitude larger than that of hydrogen amorphous silicon (a-Si;H).1) Thin film transistors (TFTs) that employ amorphous oxide semiconductors such as ZnO, In-Ga-Zn-O, or Hf-In-Zn-O (HIZO) are currently subject of intensive study owing to their high potential for application in flat panel displays. The device fabrication process involves a series of thin film deposition and photolithographic patterning steps. In order to minimize contamination, the substrates usually undergo a cleaning procedure using deionized water, before and after the growth of thin films by sputtering methods. The devices structure were fabricated top-contact gate TFTs using the a-IGZO films on the plastic substrates. The channel width and length were 80 and 20 um, respectively. The source and drain electrode regions were defined by photolithography and wet etching process. The electrodes consisting of Ti(15 nm)/Al(120 nm)/Ti(15nm) trilayers were deposited by direct current sputtering. The 30 nm thickness active IGZO layer deposited by rf magnetron sputtering at room temperature. The deposition condition is as follows: a rf power 200 W, a pressure of 5 mtorr, 10% of oxygen [O2/(O2+Ar)=0.1], and room temperature. A 9-nm-thick Al2O3 layer was formed as a first, third gate insulator by ALD deposition. A 290-nm-thick SS6908 organic dielectrics formed as second gate insulator by spin-coating. The schematic structure of the IGZO TFT is top gate contact geometry device structure for typical TFTs fabricated in this study. Drain current (IDS) versus drain-source voltage (VDS) output characteristics curve of a IGZO TFTs fabricated using the 3-layer gate insulator on a plastic substrate and log(IDS)-gate voltage (VG) characteristics for typical IGZO TFTs. The TFTs device has a channel width (W) of $80{\mu}m$ and a channel length (L) of $20{\mu}m$. The IDS-VDS curves showed well-defined transistor characteristics with saturation effects at VG>-10 V and VDS>-20 V for the inkjet printing IGZO device. The carrier charge mobility was determined to be 15.18 cm^2 V-1s-1 with FET threshold voltage of -3 V and on/off current ratio 10^9.

• 한국구조물진단유지관리공학회 논문집
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• 제24권2호
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• pp.103-110
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• 2020

본 연구는 바인더젯 3D 프린팅 출력물의 강도증진을 위하여 진공함침 후처리 공정의 적용성을 검토하였다. 또한, 출력물 크기에 따른 강도발현 한계를 확인하기 위하여 10 mm, 20 mm, 30 mm 및 40 mm 큐빅 출력물을 대상으로 침투성, 부피밀도 및 압축강도를 확인하였다. 그 결과, 진공함침 후처리 공정에서 최대압력이 증가함에 따라 후처리 용액이 출력물 내부까지 침투하게 되고 이에 따라서 침투면적률이 개선되는 것을 확인하였다. 출력물 압축강도율과 후처리 용액 침투면적률은 보정결정계수 0.992의 지수함수 형태의 상관관계를 나타내고 있다. 또한, 부피밀도가 증가하였으며 이는 후처리 용액이 내부까지 침투한 것으로 유추할 수 있다. 결론적으로 바인더젯 3D 프린팅 출력물의 강도증진을 위해서는 출력물 내부까지 후처리 용액을 침투하는 것이 필수적이며, 이를 위한 유효한 방법으로써 진공함침을 제안한다.