• Advances in Energy Research
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• v.7 no.1
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• pp.1-19
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• 2020

Energy consumption of air-conditioning and refrigeration systems is responsible for about 25 to 30% of the energy demand especially in hot seasons. This equipment is mostly electricity dependent and their use in principle affects negatively the environment. Enhancing the energy efficiency of the existing equipment is important as one of the measures to reduce environment impacts. This paper reports the results of an experimental study to evaluate the impacts of the use electronic expansion valve and variable velocity compressor on the performance of vapor compression refrigeration system. The experimental rig is composed of two independent circuits one for the vapor compression system and the other is the secondary fluid system. The vapor compression system is composed of a forced air condenser unit, evaporator, hermetic compressor and expansion elements, while the secondary system has a pump for circulating the secondary fluid, and an air conditioning heat exchanger. The manufacturer's data was used to determine the optimal points of operation of the system and consequently tests were done to evaluate the influence of variation of the compressor velocity and the opening of the expansion device on the performance of the refrigeration system. A fuzzy logic model was developed to control the rotational velocity of the compressor and the thermal load. Fuzzy control model was made in LabVIEW software with the objective of improving the system performance, stability and energy saving. The results showed that the use of fuzzy logic as a form of control strategy resulted in a better energy efficiency.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.261-262
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• 2006

$CuInS_2$ thin films were synthesized by sulpurization of Cu/In Stacked elemental layer deposited onto glass Substrates by vacuum furance annealing at temperature 200[$^{\circ}C$]. And structural and electrical properties were measured in order to certify optimum conditions for growth of the ternary compound semiconductor $CuInS_2$ thin films with non-stoichiometry composition. $CuInS_2$ thin film was well made at the heat treatment 200[$^{\circ}C$] of SLG/Cu/In/S stacked elemental layer which was prepared by thermal evaporator, and chemical composition of the thin film was analyzed nearly as the proportion of 1:1:2. Physical properties of the thin film were investigated at various fabrication conditions substrate temperature, annealing and temperature, annealing time by XRD, FE-SEM and hall measurement system. At the same time, carrier concentration, hall mobility and resistivity of the thin films was $9.10568{\times}10^{17}[cm^{-3}]$, 312.502 [$cm^2/V{\cdot}s$] and $2.36{\times}10^{-2}[{\Omega}{\cdot}cm]$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.3
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• pp.185-190
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• 2015

In this study, we fabricated the indium gallium zinc oxide (IGZO), zinc oxide (ZnO), aluminum zinc oxide (AZO). oxide and silver are deposited by magnetron sputtering and thermal evaporator, respectively transparency and energy bandgap were changed by the thickness of silver layer. To fabricate metal oxide metal (OMO) structure, IGZO sputtered on a corning 1,737 glass substrate was used as bottom oxide material and then silver was evaporated on the IGZO layer, finally IGZO was sputtered on the silver layer we get the final OMO structure. The radio-frequency power of the target was fixed at 30 W. The chamber pressure was set to $6.0{\times}10^{-3}$ Torr, and the gas ratio of Ar was fixed at 25 sccm. The silver thickness are varied from 3 to 15 nm. The OMO thin films was analyzed using XRD. XRD shows broad peak which clearly indicates amorphous phase. ZnO, AZO, OMO show the peak [002] direction at $34^{\circ}$. This indicate that ZnO, AZO OMO structure show the crystalline peak. Average transmittance of visible region was over 75%, while that of infrared region was under 20%. Energy band gap of OMO layer was increased with increasing thickness of Ag layer. As a result total transmittance was decreased.

• Korean Journal of Materials Research
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• v.9 no.2
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• pp.168-172
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• 1999

We have studied the formation of Co/Ti bilayer silicide with low resistivity and good thermal stability on the heavily boron doped $\textrm{p}^{+}$-Si region. In this paper, Co/Ti bilayer silicides were fabricated by depositing Co($150\AA$)/Ti($50\AA$) films on the clean $\textrm{p}^{+}$-Si substrates in an E-beam evaporator and performing the two step RTA process (first annealing: 650$50^{\circ}C$/20sec, second annealing: $800^{\circ}C$/20sec) in a $N_2$ambient with the pressure of $\textrm{10}^{-1}$atm. Co/Ti bilayer silicides obtained from our experiments exhibited the low resistivity of about $18\mu\Omega$-cm and the uniform thickness of about $500\AA$ without change of sheet resistance and agglomeration under the long post0annealing time up to $1000^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.189-189
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• 2010

최근 연구와 생산에 가속이 붙기 시작한 AMOLED는 모두 LTPS TFT를 사용하고 있다. LTPS TFT는 높은 전자 이동도를 가지고 있기 때문에 현재 각광 받는 AMOLED에 잘 맞는다. 하지만 LTPS TFT는 균일성이 낮고 고비용이라는 문제점이 있으며, 현재 대면적 기술이 부족한 상태이다. 극복방안으로 AMOLED를 타겟으로 하는 Oxide TFT와 a-Si TFT의 기술이 발전되고 있다. Oxide TFT는 AMOLED backplane으로 사용될 수 있는 강력한 후보 중의 하나이다. Oxide TFT는 단결정 산화물과 다결정 복합 산화물 두 가지 범주를 가지고 있다. 본 연구에서는 다결정 Oxide TFT의 하나인 ZTO TFT를 연구함으로서 Engineer의 근본적 이슈인 저비용에 초점을 맞추어 소자특성을 확인해보도록 한다. n-type wafer 에 PE-CVD 장비를 이용하여 SiNx를 120 nm 증착하고, channel layer인 ZTO 용액을 spin-coating을 이용하여 형성하였다. 균일하게 형성된 ZTO의 결정을 위하여 $500^{\circ}C$에서 1시간 동안 공기 중에서 annealing을 하였다. 과정을 거친 ZTO는 약 30 nm 두께로 형성되었다. Thermal evaporator를 이용하여 Source, Drain의 전극을 형성 하고, wafer 뒷면에는 Silver paste를 이용하여 Gate를 형성하였다. 제작된 소자를 dark room temperature 에서 측정 하였다. 측정된 소자는 우수한 전기적 특성과 0.96 cm2/Vs 인 이동도를 얻어냈다. 이러한 소자의 안정성에 따른 전기적 특성을 관측하기 위하여 상온에서 $100^{\circ}C$ 까지의 온도 스트레스를 주었다. Stress에 따른 소자는 상온에서 시작하여 온도가 올라갈수록 이동도가 낮아지고, 문턱전압 증가와 SS이 커짐을 알 수 있었다. 캐리어의 운동 매커니즘에서 온도가 올라가면 격자진동의 영향을 크게 받음으로서 캐리어의 이동도가 낮아져 전기적 특성이 낮아지는 점이 본 연구에도 적용됨을 알 수 있었다. 본 연구를 통하여 화학적 안정성을 지닌 소자라는 점과 더불어 여타 TFT공정에 비하여 현저히 낮은 공정비용을 통하여 AMOLED가 요구하는 수준의 특성에 가까운 소자를 제작할 수 있다는 것을 확인하였으며 앞으로의 추가적인 연구에 따라서 더욱 완성된 공정기술을 기대할 수 있었다.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.2
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• pp.107-112
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• 2000

$(Sr_{0.85}Ca_{0.15})TiO_3$(SCT) thin films were deposited on Pt-coated $TiO_2/SiO_2/Si$ wafer by the rf sputtering method. Experiments were conducted to investigate the electrical properties of SCT thin films with various top electrodes. Various top electrodes as Pt, Al, Ag, Cu were deposited on SCT thin films by sputter and thermal evaporator. The characteristics of C-F and C-V of SCT thin films were not obviously varied with various top electrodes, SCT thin films annealed at $600^{\circ}C$ represents as favorable capacitance characteristics than SCT thin films not annealed, and Pt top electrode have the most high capacitance. The characteristic of I-V of SCT thin films showed that Pt top electrode revealed more less leakage current density than other electrodes, had a leakage current density below 10-8$[A/cm^2]$ until 25[V] applied voltage.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.341-341
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• 2011

최근 AMOLED 구동이 가능한 소자에 대한 연구가 활발히 진행중이다. AMOLED구동 가능소자는 LTPS TFT, a-Si TFT, OTFT, Oxide TFT가 있으며 그 중에서 현재 대부분 LTPS TFT를 사용하고 있다. LTPS TFT는 높은 전자 이동도와 안정성을 가지고 있기 때문에 현재 각광 받는 AMOLED에 잘 맞는다. 하지만 LTPS TFT는 고비용, 250$^{\circ}C$ 이상의 공정온도, Substrate가 Glass, Metal로 제한 된다는 문제점이 있으며, 균일성이 낮고 현재 대면적 기술이 부족한 상태이다. 해결방안으로 AMOLED를 타겟으로 하는 Oxide TFT 기술이 떠오르고 있다. Oxide TFT는 이동도가 높고 저온공정이 가능하며 Substrate로 Plastic 기판을 사용할 수가 있어 차후에 Flexible 소자로서의 적용이 가능하다. 또한 기존의 진공장비 사용대신 용액공정이 가능하여 장비사용시간 및 절차를 단축시킬 수 있어 비용적인 유리함을 가지고 있다. Oxide TFT는 단결정 산화물과 다결정 복합 산화물 두 가지 범주를 가지고 있다. Oxide TFT의 재료물질은 ZnO, ZTO, IZO, SnO2, Ga2O3, IGO, In2O3, ITO, InGaO3(ZnO)5, a-IGZO이 있다. 본 연구에서는 산화물질 중 하나인 ZTO를 이용하여 TFT 소자를 제작하였다. 산화물 특성상 열처리 온도에 따라 형성되는 결정의 정도가 다르기 때문에 온도 및 시간 변수에 따른 ZTO의 특성변화에 초점을 맞추어 연구함으로서 최적화된 조건을 찾고자 실험을 진행하였다. 실험을 위한 기판으로 n-type wafer을 사용하였다. PE-CVD 장비를 이용하여 SiNx를 120 nm 증착하고, ZTO 용액을 spin-coating을 이용하여 channel layer을 형성하였다. 균일하게 형성된 ZTO의 결정을 위하여 200$^{\circ}C$, 300$^{\circ}C$, 400$^{\circ}C$, 500$^{\circ}C$에서 1시간, 3시간, 6시간, 10시간의 온도 및 시간 변수를 두어 공기 중에서 열처리 하였다. ZTO는 약 30 nm 두께로 형성되었다. Thermal evaporator를 이용하여 Source, Drain의 알루미늄 전극을 형성하고, wafer 뒷면에는 Silver paste를 이용하여 Gate전극을 만들었다. 제작된 소자를 dark room temperature에서 측정하였다.

• Macromolecular Research
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• v.10 no.4
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• pp.204-208
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• 2002

A linear rod-like molecule, bis[4-(1,3-octadynyl)phenyl] terephthalate (2), consisting of two diacetylenic groups, was prepared. The unsymmetric diacetylene was prepared by the Cadiot-Chodkiewicz coupling reaction of 1-bromohexyne with 4-ethynylphenol and linked to a benzene core by an esterification reaction with terephthaloyl chloride in tetrahydrofuran. The thin film (200 nm thickness) of compound 2 was fabricated by the physical vapor deposition on a glass plate with a thermal evaporator. In the X-ray diffraction (XRD) study, the vapor deposited film on the glass plate showed peaks with d spacings of 19.4, 5.7, and 4.5 $\AA$. This XRD pattern was quite different from that observed for compound 2 isolated by recrystallization from methylene chloride/hexane. The vapor deposited film was polymerized by UV irradiation. Photopolymerization was carried out through a photomask, resulting in a patterned image, where the irradiated part became isotropic.

• Solar Energy
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• v.12 no.3
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• pp.37-46
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• 1992

An experimental study was carried out to investigate the performance of a latent heat storage system using paraffin wax as the phase change material. A thermosyphon was employed to transfer heat from the hot ethylene glycol flowing across the evaporator section of the thermosyphon into the wax. In order to increase the effective thermal conductivity of wax, layers of copper wire mesh were immersed in the wax. Experiments were run for volume ratios of 2%, 3%, and 4%, varying mass flow rate of ethylene glycol in each case. Some of the important results are as follows : (1) The wire mesh enhanced the conductive hea transfer and thus, helped even out the temperature distribution in the wax : (2) The increase of the number of layers of wire mesh increased the conduction. However, it also resulted in increasing the resistance to the convective motion of liquefied wax : and (3) There is an optimal number of layers of wire mesh, maximizing the performance of the storage system, which occurred at a volume ratio of $3{\sim}4%$ in the present study.

• Journal of the Korean Magnetics Society
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• v.8 no.2
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• pp.79-85
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• 1998

The $[Ni_{80}Fe_{20}/Cu/Co/Cu]$ multilayers were grown by evaporation technique, and according to magnetic exchange coupling relation, magnetoresistance ratio and magnetization curve were studied by Co inserting $Ni_{80}Fe_{20}/Cu$ interface. Insertion of Co layer to the antiferromagnetically coupled system, i. e $t_{Cu} = 25\;{\AA}$, decrese the MR ratio contrary to previous reports. However the insertion to the ferromagneticalyl coupled $(t_{Cu} = 27\;{\AA})$ and the noncoupled $(t_{Cu} = 47\;{\AA})$ systems increase the ratio to 3.5 % and 6 % respectively. The results imply that the insertion change the magnetic exchange coupling state as well as the spin dependent scattering of conduction electrons. Besides, insertion of Co layer between Cu and $Ni_{80}Fe_{20}$ layer enhaces thermal stability to the 300 $^{\circ}C$, which indicates that insertion of Co has a role of the effective diffusion barrier.