• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1529-1534
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• 2012

In this study, tensile tests for 12-${\mu}m$-thick copper thin foils were performed by using the DIC method. The DIC method provided precise stress-strain curves for thin film materials, and a commercial inkjet printer can be simply and effectively used for printing speckle patterns on the specimen of Cu thin films whose surface contrast is too low to apply the DIC method. The mechanical properties of Cu thin foils obtained in this study are as follows: elastic modulus E = 89.2 GPa, 0.2% offset yield stress $S_{0.2%}$= 232.8 MPa, tensile strength $S_u$= 319.2 MPa, elongation at fracture ${\varepsilon}_f$=16.8 %, and Poisson's ratio ${\nu}$= 0.34.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.8
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• pp.745-750
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• 2017

Tension tests for copper thin films with thickness of $12{\mu}m$ were performed by using a digital image correlation method based on consecutive digital images. When calculating deformation using digital image correlation, a large deformation causes errors in the calculated result. In this study, the calculation procedure was improved to reduce the error, so that the full field deformation and the strain of the specimen could be accurately and directly measured on its surface. From the calculated result, it can be seen that the strain distribution is not uniform and its variation is severe, unlike the distribution in a common bulk specimen. This might result from the surface roughness introduced in the films during the fabrication process by electro-deposition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.169-174
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• 2022

This study is to verify the feasibility of SiC single crystal growth using recycled SiC powder. The fundamental physical properties such as particle size, shape, composition and impurities of the recycled powder were analyzed, and the sublimation behavior occurring inside the reactor were predicted using the basic data. As a result of comprehensive judgment, the physical properties of the recycled powder were suitable for single crystal growth, and single crystal growth experiments were conducted using this. 100 mm 4H-SiC single crystal ingot with a height of 25 mm was grown without polytype inclusion. In the case of micro-pipe density was 0.02 ea/cm² and resistivity characteristics was 0.015~0.020 ohm·cm², commercial level quality was obtained, but additional analysis related to dislocation density and stacking faults is required for device application.

• Journal of the Korean Magnetics Society
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• v.21 no.2
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• pp.77-82
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• 2011

The use of soft magnetic materials have been increasing in the various industrial fields according to the increasing demand for high performance, automatic, miniaturing equipments in the recent our life. In this study, we investigated the effect of factors on the core loss and magnetic properties of electrical steel and soft magnetic composites. Furthermore, we reviewed the major efforts to reduce the core loss and improve the soft magnetic properties in the two main soft magnetic materials. Domain purification which results from reduced density of defects in cleaner electrical steels is combined with large grains to reduce hysteresis loss. The reduced thickness and the high electrical conductivity reduce the eddy current component of loss. Furthermore, the coating applied to the surface of electrical steel and texture control lead to improve high permeability and low core loss. There is an increasing interest in soft magnetic composite materials because of the demand for miniaturization of cores for power electronic applications. The SMC materials have a broad range of potential applications due to the possibility of true 3-D electromagnetic design and higher frequency operation. Grain size, sintering temperature, and the degree of porosity need to be carefully controlled in order to optimize structure-sensitive properties such as maximum permeability and low coercive force. The insulating coating on the powder particles in SMCs eliminates particle-to-particle eddy current paths hence minimizing eddy current losses, but it reduces the permeability and to a small extent the saturation magnetization. The combination of new chemical composition with optimum powder manufacturing processes will be able to result in improving the magnetic properties in soft magnetic composite materials, too.

• Journal of the Korean Vacuum Society
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• v.17 no.5
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• pp.466-472
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• 2008

Purple Gold is the alloy consisting of 78wt%Au-22wt%Al, and is expressed as a chemical formula, $AuAl_2$. Lately it is being used for the material of accessories or the decorative ornaments, being one of the colored golds having the peculiar purple color, like White Gold and Pink Gold. Purple Gold has the weak point in shaping through casting process due to the bad malleability and castability, being the intermetalic compound of Au and Al. Therefore, it is possible to produce the final product only by the cutting and the grinding process or to use it as a decorative coat with the thin film evaporation. This study implemented two kinds of thin film experiments. One is the case that heat treatment was made after Au and Al deposition evaporated separately with a weight ratio 78:22 on the 200nm$SiO_2$/Si substrate. The other is the case that the surface deposition was made through the vacuum evaporation, keeping the glass substrate temperature remain room temperature, using the bulk $AuAl_2$ as a source. The final film property was measured, focusing on the Purple Gold's color and thickness through the bare eye inspection, the microstructure analysis, the surface resistance analysis, the color difference analysis, and XRD analysis. Purple Gold was not formed, as the excessive surface agglomeration occurred, in case of being produced and treated thermally with 12.5nmAu/40nmAl/200nm$SiO_2$/Si structure. Our results suggest that of Purple Gold films, showing the same purple color as the bulk's, were successfully deposited with the direct thermal evaporation from the $AuAl_2$ bulk source.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.9-15
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• 2008

Mokumegane is one of the sophisticated metal craft techniques enabling wood grain surface effect. To embody the mokumegane, an ingot of well-bonded stacked metal plates has been required. Traditionally prepared mokumegane ingots were bonded using charcoal which enables reduction atmosphere, but sometimes end up with collapse of bonding interface due to the lack of reliable process control. We proposed a systematic vacuum direct bonding process for ingots. First, we confirmed copper//copper homogeneous plate bonding at $900^{\circ}C$ by applying uniaxial press of 2.5kg. We observed 80min required to obtain 90%-bonding ratio and the diffusion coefficient would be enhanced up to 100 times due to surface effect. Second, by considering enhanced diffusion behavior, we also obtained optimum bonding condition in copper/silver heterogeneous plates that ensures 90%-bonding ratio at $700^{\circ}C$ for 10min with apply uniaxial press. A 7-layered copper/silver ingot is prepared successfully, and eventually the prototype mokumegane cases for mobile phone were fabricated with these ingot.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.21-21
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• 2006

21세기 정보통신 및 관련 소재의 연구방향은 새로운 기능성 확보, 극한적 제어성, 복합 및 융합이라는 경향으로 발전해 가고 있다. 반도체 기술 분야에서 현재의 공정적 한계를 극복하고 새로운 기능성을 부여하기 위해 나노 합성과 배열을 기본으로 하여 bottom-up 방식의 나노소자 구현이 큰 주목을 받고 있다. 나노선의 경우 나노 스케일의 dimension, 양자 제한 효과, 우수한 결정성, self-assembly, internal stress 등 기존 벌크형 소재에서 발견할 수 없는 새로운 기능성이 나타나고 있어 바이오, 에너지, 구조, 전자, 센서 등의 분야에서의 활용이 가능하다. 현재 국내외적으로 반도체 나노선으로 널리 연구되고 있는 재료는 ZnO, $SnO_2$, SiC 등이 중심이 되고 있다. 이중 ZnO 나 노선의 합성을 위해서는 thermal CVD, MOCVD, PLD, wet-chemical 등 다양한 방법이 사용되고 있다. 특히 MOCVD 방법에 의해 수직 정렬된 ZnO 나노막대를 성장할 수 있다. 이러한 나노막대는 MO 원료 및 산소 공급량을 적절히 제어함으로서 수직 배향 및 나노선의 구경 제어가 가능하며, 나노 막대의 크기 제어와 관련해서는 반응 관내의 DEZn 와 $O_2$의 양을 변화시켜 구조체의 크기를 수 십 ~ 수 백 나노미터의 크기로 제어할 수 있다. 본 연구는 이러한 ZnO 나노선의 성장과정에서 $210^{\circ}C$ 이하의 저온에서 성장한 ZnO 버퍼층을 이용해 나노구조의 형상을 제어하고자 하였다. 특히 ZnO 저온 버퍼층의 두께에 따라 나노막대의 직경변화, 수직배향성, 형상변화의 제어가 가능하였다. 나노막대의 특성 평가는 TEM, SEM, PL, XRD 등을 이용하여 구조적, 결정학적, 광학적 특성을 분석하였다.

• Journal of Digital Contents Society
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• v.14 no.1
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• pp.35-40
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• 2013

The use of slurry with a mix of abrasives and coolant for making Wire Saw in the photovoltaic industry has sharply increased with the semiconductor wafer. In this paper, the slurry was isolated, purified and dried by microwave drying method with high-purity silicon carbide powder obtained through chemical processing. Dried slurry bulk was first pulverized and chemical treatment was applied to produce powder. The produced slurry powder was then analyzed by going through the following analysis; thermal analysis, particle size analyses: SEM shots, elemental analysis, XRF and XRD. The results of this study found the recovery rate of the power obtained though the chemical processing to be higher than the one obtained from mineral processing. The results anticipate infrastructure building and active responses to increasingly stronger domestic and international environmental regulations through the integration and recycling of large amounts of slurry in the photovoltaic industry.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.387-387
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• 2007

기능성 나노소자를 구현할 수 있는 나노 소재로 0차원 구조의 양자점(quantum dot)과 1차원 구조의 양자선 및 나노선(nanorod)이 제안되고 있다. 나노선의 경우 나노스케일의 dimension, 앙자 제한 효과, 탁월한 결정성, self-assembly, internal stress등 기존의 벌크형 소재에서 발견할 수 없는 새로운 기능성이 나타나고 있어서 바이오, 에너지, 구조, 전자, 센서 등의 분야에서 활용되고 있다. 현재 국내외적으로 널리 연구되고 있는 나노선으로는 Si 및 Ge, $SnO_2$, SiC, ZnO 등이 있으며 특히, ZnO는 우수한 물리적 전기적 특성과 함께 나노선으로의 합성이 비교적 쉬워 주목받고 있는 재료이다. ZnO의 합성방법으로는 thermal CVD, MOCVD, PLD, wet-chemistry 등 다양한 방법이 사용되고 있다. 특히 MOCVD 법은 수직 정렬된 ZnO 나노막대를 합성하기가 매우 용이하다. 본 실험에서는 자체개발된 MOCVD 장비를 이용한 일차원 ZnO 나노선을 성장하였다. 이러한 ZnO 나노선의 성장은 사파이어 기판과 실리콘 기판 위에서 이루어졌으며 기판의 종류와 격자상수 불일도에 따른 상이한 성장과정을 온도에 따른 나노선 성장에서 관찰할 수 있었다. 사파이어 기판의 경우, 240도의 온도에서는 박막형상을 지닌 ZnO가 온도가 320도 이상으로 상승하면서 나노선으로 변함을 보였고, 실리콘 기판의 경우 380도 이상에서 기울기률 가진 나노선을 관찰하였으며, 420도에서는 나노선을 관찰 할 수 없었다. 또한 PL 장비를 이용한 PL 강도와 성장과정을 연관하여 생각하였을 때, 나노선의 기물기가 PL 강도비과 연관성을 가진다는 것을 측정을 통해 확인하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.143-143
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• 2003

현대 산업이 발전함에 따라 다양한 기기들의 초소형화가 급속히 진행되고 있다. 이러한 요구에 부응하기 위하여 미세구동소자(Microelectromechanical system)의 개발이 많은 연구 그룹들에 의해서 이루어지고 있다. 미세구동소자에 응용을 하기 위해 개발되어지고 있는 여러 가지 소재들 중 $\ulcorner$형상기억합금 $\lrcorner$은 기존의 바이메탈이나 피에조 소자에 비하여 작동거리가 우수하기 때문에 그 가능성을 인정받고 있지만, 벌크재료는 느린 냉각속도 때문에 반응속도가 느린 단점이 있기 때문에 박막화 할 필요성이 있다. 이러한 이유로 여러 그룹들에 의해 형상기억합금의 박막화가 시도되고 있으나, 조성에 의해 특성의 변화가 심한 형상기억합금의 정밀한 조성제어가 힘들다고 알려져 있다. 몇몇 연구 그룹에서 RF magnetron sputtering법을 이용하여 Ti-Ni합금 박막을 성공적으로 제조하였다는 보고가 있지만, 타겟 조성 및 형태 등의 정밀한 제어가 필요하므로 3원 합금 박막 등을 제조할 경우에는 또 다시 타겟의 조건을 정밀하게 제어해야 할 필요성이 있다. 따라서 본 연구에서는 산화물 박막등의 제조에 있어서 타겟 조성과 제조된 박막 조성이 잘 일치하여 조성제어가 쉽게 이루어진다고 알려져 있는 PLD법을 도입하여 형상기억합금 박막제조에 적용가능한지를 검토하는 것을 목적으로 하였다.