• Journal of Welding and Joining
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• v.26 no.3
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• pp.30-36
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• 2008

A flip-chip bonding system using IR laser with a wavelength of 1064 nm was developed and associated process parameters were analyzed using Taguchi methods. An infrared laser beam is designed to transmit through a silicon chip and used for transferring laser energy directly to micro-bumps. This process has several advantages: minimized heat affect zone, fast bonding and good reliability in the microchip bonding interface. Approximately 50 % of the irradiated energy can be directly used for bonding the solder bumps with a few seconds of bonding time. A flip-chip with 120 solder bumps was used for this experiment and the composition of the solder bump was Sn3.0Ag0.5Cu. The main processing parameters for IR laser flip-chip bonding were laser power, scanning speed, a spot size and UBM thickness. Taguchi methods were applied for optimizing these four main processing parameters. The optimized bump shape and its shear force were modeled and the experimental results were compared with them. The analysis results indicate that the bump shape and its shear force are dominantly influenced by laser power and scanning speed over a laser spot size. In addition, various effects of processing parameters for IR laser flip-chip bonding are presented and discussed.

• Korean Journal of Materials Research
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• v.22 no.6
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• pp.280-284
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• 2012

Bismuth antimony telluride (BiSbTe) thermoelectric materials were successfully prepared by a spark plasma sintering process. Crystalline BiSbTe ingots were crushed into small pieces and then attrition milled into fine powders of about 300 nm ~ 2${\mu}m$ size under argon gas. Spark plasma sintering was applied on the BiSbTe powders at 240, 320, and $380^{\circ}C$, respectively, under a pressure of 40 MPa in vacuum. The heating rate was $50^{\circ}C$/min and the holding time at the sintering temperature was 10 min. At all sintering temperatures, high density bulk BiSbTe was successfully obtained. The XRD patterns verify that all samples were well matched with the $Bi_{0.5}Sb_{1.5}Te_{3}$. Seebeck coefficient (S), electric conductivity (${\sigma}$) and thermal conductivity (k) were evaluated in a temperature range of $25{\sim}300^{\circ}C$. The thermoelectric properties of BiSbTe were evaluated by the thermoelectric figure of merit, ZT (ZT = $S^2{\sigma}T$/k). The grain size and electric conductivity of sintered BiSbTe increased as the sintering temperature increased but the thermal conductivity was similar at all sintering temperatures. Grain growth reduced the carrier concentration, because grain growth reduced the grain boundaries, which serve as acceptors. Meanwhile, the carrier mobility was greatly increased and the electric conductivity was also improved. Consequentially, the grains grew with increasing sintering temperature and the figure of merit was improved.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.110-115
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• 2016

We prepared a working electrode (WE) coated with 0 ~ 50 nm-thick indium gallium zinc oxide(IGZO) by using RF sputtering to improve the energy conversion efficiency (ECE) of a dye sensitized solar cell (DSSC). Transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) were used to analyze the microstructure and composition of the IGZO layer. UV-VIS-NIR spectroscopy was used to determine the transparency of the WE with IGZO layers. A solar simulator and a potentiostat were used to confirm the photovoltaic properties of the DSSC with IGZO layer. From the results of the microstructural analysis, we were able to confirm the successful deposition of an amorphous IGZO layer with the expected thickness and composition. From the UV-VIS-NIR analysis, we were able to verify that the transparency decreased when the thickness of IGZO increased, while the transparency was over 90% for all thicknesses. The photovoltaic results show that the ECE became 4.30% with the IGZO layer compared to 3.93% without the IGZO layer. As the results show that electron mobility increased when an IGZO layer was coated on the $TiO_2$ layer, it is confirmed that the ECE of a DSSC can be enhanced by employing an appropriate thickness of IGZO on the $TiO_2$ layer.

• Economic and Environmental Geology
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• v.19 no.spc
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• pp.121-130
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• 1986

In the Janggun mine, stannite occurs as anhedral grains, up to 500 micrometer in long dimension, closely associated with sphalerite, chalcopyrite, arsenopyrite, pyrrhotite, galena and rhodochrosite in the periphery of the South ore body. In reflected light, stannite is grayish yellow green in color and exhibits moderate bireflectance and strong anisotropism without any intenal reflections. Reflection; Rmax. =29.0, Rmin. =27.8 percent at a wavelength of 560nm, and VHN; 219~244kg/mm at a 50g load. The chemical composition on the average from 35 spot analyses by electron microprobe is, Cu 28.0, Fe 12.7, Zn 2.9, Mn 0.2, Sn 25.8, S 30.3, sum 99.9 (all in weight percent); the corresponding chemical formula as calculated on the basis of total atoms=8 is, Cu 1.88 Fe 0.97 Zn 0.19 Mn 0.02 Sn 0.93 S 4.01, which fulfills approximately the ideal formula of $Cu_2FeSnS_4$. The strongest reflections on the X-ray diffraction patterns are; $3.10{\AA}$ (10) (112), $2.72{\AA}$ (5) (020, 004), $1.922{\AA}$ (5) (024), $1.642{\AA}$ (3) (132), $1.244{\AA}$ (3) (143, 136, 235), $1.111{\AA}$(3) (244), $0.958{\AA}$ (1) (048, 422), the patterns are identical with those of literature. From the textural evidence of the microscopic observation, the mineral is considered to have been formed at the middle stage of hydrothermal lead-zinc-silver mineralization.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.5
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• pp.300-305
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• 2015

$WO_3$, $SiO_2$, and $TiO_2$ films with hydrophilic property are deposited by rf-magnetron sputtering. Their wettability is strongly depends on the presence or absence of the oxygen plasma etching on the glass substrates. The $TiO_2$ film of 50 nm-thick on the plasma etched glass shows a water contact angle (WCA) below $5^{\circ}$ which means a super-hydrophilic surface. However, WCA values are gradually degraded when the films are exposed under atmosphere, especially $WO_3$. In order to improve hydrophilic property, the degraded films can be again recovered by UV illumination for 10 sec using UV-light and the $TiO_2$ film shows a super-hydrophilic surface about $3^{\circ}$.

• Korean Journal of Materials Research
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• v.22 no.2
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• pp.86-90
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• 2012

Insoluble catalytic electrodes were fabricated by RF magnetron sputtering of Pt on Ti substrates and the performance of seawater electrolysis was compared in these electrodes to that is DSA electrodes. The Pt-sputtered insoluble catalytic electrodes were nearly 150 nm-thick with a roughness of $0.18{\mu}m$, which is 1/660 and 1/12 of these values for the DSA (dimensionally stable anodes) electrodes. The seawater electrolysis performance levels were determined through measurements of the NaOCl concentration, which was the main reaction product after electrolysis using artificial seawater. The NaOCl concentration after 2 h of electrolysis with artificial seawater, which has 3.5% NaCl normally, at current densities of 50, 80 and 140 mA/$cm^2$ were 0.76%, 1.06%, and 2.03%, respectively. A higher current density applied through the electrodes led to higher electrolysis efficiency. The efficiency reached nearly 58% in the Pt-sputtered samples after 2 h of electrolysis. The reaction efficiency of DSA showed higher values than that of the Pt-sputtered insoluble catalytic electrodes. One plausible reason for this is the higher specific surface area of the DSA electrodes; the surface cracks of the DSAs resulted in a higher specific surface area and higher reaction sites. Upon the electrolysis process, some Mg- and Ca-hydroxides, which were minor components in the artificial seawater, were deposited onto the surface of the electrodes, resulting in an increase in the electrical resistances of the electrodes. However, the extent of the increase ranged from 4% to 7% within an electrolysis time of 720 h.

• Korean Journal of Materials Research
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• v.22 no.4
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• pp.202-206
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• 2012

$CoSi_2$ was formed through annealing of atomic layer deposition Co thin films. Co ALD was carried out using bis(N,N'-diisopropylacetamidinato) cobalt ($Co(iPr-AMD)_2$) as a precursor and $NH_3$ as a reactant; this reaction produced a highly conformal Co film with low resistivity ($50\;{\mu}{\Omega}cm$). To prevent oxygen contamination, $ex-situ$ sputtered Ti and $in-situ$ ALD Ru were used as capping layers, and the silicide formation prepared by rapid thermal annealing (RTA) was used for comparison. Ru ALD was carried out with (Dimethylcyclopendienyl)(Ethylcyclopentadienyl) Ruthenium ((DMPD)(EtCp)Ru) and $O_2$ as a precursor and reactant, respectively; the resulting material has good conformality of as much as 90% in structure of high aspect ratio. X-ray diffraction showed that $CoSi_2$ was in a poly-crystalline state and formed at over $800^{\circ}C$ of annealing temperature for both cases. To investigate the as-deposited and annealed sample with each capping layer, high resolution scanning transmission electron microscopy (STEM) was employed with electron energy loss spectroscopy (EELS). After annealing, in the case of the Ti capping layer, $CoSi_2$ about 40 nm thick was formed while the $SiO_x$ interlayer, which is the native oxide, became thinner due to oxygen scavenging property of Ti. Although Si diffusion toward the outside occurred in the Ru capping layer case, and the Ru layer was not as good as the sputtered Ti layer, in terms of the lack of scavenging oxygen, the Ru layer prepared by the ALD process, with high conformality, acted as a capping layer, resulting in the prevention of oxidation and the formation of $CoSi_2$.

• Korean Journal of Pharmacognosy
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• v.44 no.4
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• pp.362-367
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• 2013

Ojeok-san has been commonly used to treat low back pain disease. We performed the experiments on simultaneous analysis of 11 compounds and antioxidant effects of Ojeok-san. A HPLC method was established for simultaneous analysis of 11 compounds. The detection wavelengths were set at 230, 254, 280, 320, and 330 nm. The detected 11 compounds from Ojeok-san water extract showed good linearity($r^2{\geq}0.9997$). Limit of detection(LOD) and limit of quantification(LOQ) were 0.04-0.87 ${\mu}g/mL$ and 0.13-2.63 ${\mu}g/mL$, respectively. The antioxidant effects of Ojeok-san water extract were investigated by DPPH and ABTS assays. Ojeok-san water extract significantly increased the DPPH and ABTS radical scavenging effects in a dose-dependent manner. The $RC_{50}$ value of Ojeok-san on DPPH radical was 284.71 ${\mu}g/mL$ and that of ABTS radical was 96.16 ${\mu}g/mL$.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.238-238
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• 2012

Ag (silver)의 일함수는 T-OLED (Top Emission Organic Light Emitting Diode)의 전극소자로 사용하기에는 다소 낮다는 단점이 있다(~4.3 eV). 이러한 단점을 해결하기 위한 대안으로 Ag 박막의 표면을 플라즈마 처리, UV 처리 및 열처리를 통하여 일함수를 높이는 연구가 진행 되어왔다(>5.0 eV). 하지만 현재의 대부분 연구는 후 처리된 박막의 일함수에 초점을 맞춰 연구가 진행 되어 박막의 nano-mechanical property에 대한 연구는 매우 부족하다. 따라서 본 논문에서는 AgOx 박막의 nano-mechanical property에 초점을 맞춰 분석을 실시하였다. 연구에 사용된 샘플은 Ag 박막을 유리기판 위에 rf-magnetron sputter 장치를 이용하여 100 W의 power로 150 nm 두께로 증착하였다. 증착된 Ag 박막은 $O_3$ 발생 UV 램프를 이용하여, 다양한 시간동안 UV 처리하였다(0~9분). 증착된 샘플은 Four-point probe, nanoindenter 장비를 이용하여 nano-mechanical property를 분석하였다. 실험 결과 UV 처리 시간이 0, 1분에서 면저항이 0.16, 0.50 ${\Omega}$/sq로 급격한 변화가 나타났으나, 반면 3분 이후 9분의 샘플의 경우, 0.55 ${\Omega}$/sq에서 0.24, 0.20, 0.15 ${\Omega}$/sq로 감소하여 전기적 특성변화를 볼 수 있었다. 또한 nanoindenting 결과 UV 처리한 박막의 극 표면 경도 값의 변화는 0~5분 처리한 샘플의 경우, 물리적인 경도가 증가하는 형태를 보이며 UV 처리를 5분간 했을때 7.89 GPa로 최고의 경도를 가진다. 그 이후부터는 6.97, 3.46 GPa의 결과로 박막의 경도가 감소되는 결과를 얻었다. 이러한 결과로부터 Ag 박막의 후처리에 따른 Ag 물질의 산화 및 결정상태에 따라 박막 내에 존재하는 residual stress를 분석할 수 있다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.105.2-105.2
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• 2010

석탄의 직접 연소 대신 고온/고압의 조건에서 불완전연소 및 가스화 반응을 통하여 일산화탄소(CO)와 수소($H_2$)가 주성분인 합성가스를 제조하여 이용하는 석탄 가스화 기술은 현실적인 에너지원의 확보를 위한 방법인 동시에 이산화탄소를 저감할 수 있는 기술이라 할 수 있다. 따라서, 본 연구에서는 non-slagging 방식의 pilot급 분류층 석탄가스화기를 대상으로 고압 미분탄공급장치, 합성가스 냉각장치, 고온 집진장치 등을 연계하여 상용급 석탄가스기와 유사한 $1,300^{\circ}C$, 20 kg/$cm^2$의 운전조건에서 미분탄의 안정적인 공급을 통한 양질의 합성가스 제조 및 제조된 합성가스의 분기 공급특성 시험을 진행하였다. 그리고, 고압 미분탄공급장치는 공급호퍼에 저장된 미분탄을 고온/고압 조건으로 운전되는 석탄가스화기에 공급하기 위한 설비로서, 이러한 고압 미분탄공급장치를 이용한 기류수송 방식의 미분탄 공급 기술은 가스화기 설계 및 운전제어 기술과 더불어 석탄가스화기 시스템의 안정적 연속운전을 위한 가장 핵심적인 기술 중 하나라고 할 수 있다. 따라서, 본 연구에서는 아역청탄인 인도네시아 ABK탄을 대상으로 향후 dense phase 고압 기류수송을 목적으로 하는 고압 미분탄공급장치의 성능특성을 시험을 진행하였는데, 시험 결과 73 kg/h 조건에서 20 kg/$cm^2$의 가스화기에 대한 안정적인 미분탄 공급특성을 확인할 수 있었으며, 이러한 미분탄 공급 조건에서 CO 40～45%, $H_2$ 16~20%, $CO_2$ 5~8% 조성의 양질의 합성가스를 평균적으로 $230{\sim}50Nm^3/h$ 안정적으로 제조할 수 있었다.