• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.7 s.361
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• pp.1-8
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• 2007

The DC characteristics of GaAs Gunn diode are investigated as a preliminary study on the planar grade gap injector GaAs Gunn diode which is the transferred electron device with high output power and dc-rf conversion efficiency. The Gunn devices we fabricated were confirmed to have the DC characteristics of negative differential resistance(NDR). We discussed the nature of the NDR effect, including the electron intervalley transfer; the NDR effect was examined for six different cathode radii.

• Journal of the Semiconductor & Display Technology
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• v.7 no.2
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• pp.59-62
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• 2008

The Lifetime of OLEDs by ITO/glass substrates cleaning method and cathode deposition method were investigated in the fabrication of green light emitting OLEDs with $Alq_3$-C545T fluorescent system. In our experiments, the optimum cleaning method was obtained at last processing of boiling IPA(isopropyl alcohol). And the optimum deposition methode was obtained at 3 steps deposition rate of Al. The deposition rate of 3 steps progressed changing from $0.5\AA$/sec to $3\AA$/ sec. The green light emitting OLED with plasma treatment at 150W for 2 minutes showed the highest luminance and efficiency of 20000 cd/$m^2$ and 16 lm/W. On the contrary, the OLED device without plasma treatment showed much lower performance with the luminance and efficiency of 3500 cd/$m^2$ and 2 lm/W.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.368-373
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• 2004

To improve the conventional cathode-supported tubular solid oxide fuel cell (SOFC) from the viewpoint of low cell power density, expensive fabrication process and high operation temperature, the anode-supported tubular solid oxide fuel cell was investigated. The anode tube of Ni-8mol% $Y_2$O$_3$-stabilized $ZrO_2$ (8YSZ) was manufactured by extrusion process, and, the electrolyte of 8YSZ and the multi-layered cathode of $LaSrMnO_3$(LSM)ILSM-YSZ composite/$LaSrCoFeO_3$ were coated on the surface of the anode tube by slurry dip coating process, subsequently. Their cell performances were examined under gases of humidified hydrogen with 3% water and air. In the thermal cycle condition of heating and cooling rates with $3.33^{\circ}C$/min, the anode-supported tubular cell showed an excellent resistance as compared with the electrolyte-supported planar cell. The optimum hydrogen flow rate was evaluated and the air preheating increased the cell performance due to the increased gas temperature inside the cell. In long-term stability test, the single cell indicated a stable performance of 300 mA/$\textrm{cm}^2$ at 0.85 V for 255 hr.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.5
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• pp.484-492
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• 2012

The TMS(Thermal Management System) heater in a fuel cell vehicle has been developed to prevent a decline of fuel cell durability and cold start durability. Main functions of the COD(Cathode Oxygen Depletion) heater are depletion of oxygen in a cathode as heat energy and consumption of electric power for rapid warming up of a fuel cell stack. This paper covers subjects including the design specification of a heater, heater controller for detection of overheat and reliability assessment including coolant pressure cycle test of a heater. To verify the design concept, burst pressure and deformation analysis of plastic housing were carried out. Also, temperature distribution analysis of heater surface and coolant inside of housing were carried out to verify the design concept. By designing the plastic housing instead of a steel housing, the 30% weight lightening and 50% cost reduction were attained. A module-based design of a TMS system including a heater or reducing the watt density of a heater is a problem to be solved in the near future work.

• Journal of the Korean institute of surface engineering
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• v.41 no.3
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• pp.94-101
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• 2008

A new convenient magnet array module is designed to investigate effects of magnetic field array on magnetron discharge characteristics. Magnetic field analysis showed good agreement of measured discharge region by a CCD device which has a high quantum efficiency over visible wavelength range. OES (optical emission spectroscopy) showed major emission peaks are from electronic transitions in 400 nm range and 800 nm range. Effects of driving voltage characteristics were analyzed in a point of electron drift trajectories and ionizing collision frequencies. Pulsed dc with a fast rising and falling time was analyzed to have potential to increase ionization collisions by putting a burst of hot electrons and to raise sheath potential. From measured voltage and current waveform, maximum of -1000 V peak was generated with $-400\;V_{rms}$ conditions. Possibility of a properly designed magnetron cathode was shown to be used as a melting device. Cu was successfully melted with power density of a several tens of $W/cm^2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.63-63
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• 2000

Deep submicron device contact hole에서의 bottom step coverage의 향상 및 SALICIDE공정의 필요성에 의해 collimated sputtering 및 ionized sputtering 등의 다양한 증착방법이 연구되어왔다. 반도체소자의 고집적화 및 미세화에 따라서 기존의 증착방법보다 더 높은 throughput을 가진 새로운 증착방법의 필요성이 대두되고 있다. Collimated sputtering방식으로 증착한 박막의 경우에는 증착속도가 느리고 collimator의 사용기간에 따른 공정조건의 변화가 단점으로 작용하였고 새로이 ionzied sputtering방식이 개발되었다. ionzied sputtering방식은 증착되는 금속 입자를 이온화시키고 기판에 바이어스를 걸어서 증착되는 입자의 방향성 및 증착속도의 향상을 얻을 수 있었다. 하지만 고집적도가 더욱 증가함에 따라서 더 높은 박막의 증착속도, bottom step coverage의 향상, 방향성의 향상과 더불어 증착되는 입자의 이온화 율의 증가 및 기존의 증착방식에 의한 박막보다 향상된 물성을 가진 박막증착의 필요성에 의해 hollow cathode magnetron sputtering방식이 연구되었다. HCM방식으로 titanium 박막을 증착하여 collimated sputtering 및 ionize sputtering 방식으로 증착한 titanium 박막과 물성을 비교해서 증착방식에 따른 박막물성의 차이를 연구하였다. 증착전에 기판온도는 30$0^{\circ}C$를 유지하였고 base pressure는 5.0$\times$10-9torr, working pressure는 5.7m torr로 유지하였다. power는 30kW를 가하여 50nm두께의 titanium박막을 증착하였다. 증착된 박막의 미세구조는 TEM 및 XRD로 분석하였다. HCM방식으로 증착한 titanium박막은 5nm두께의 비정질 층이 관찰되었고 ionized sputtering방식으로 증착한 titatnium박막에서 나타나는 것으로 보고된 silicon (002)와 titanium (0002) eledtron diffraction spot사이의 (10-10)spot은 관찰되지 않았다. 박막은 크고 작은 grain의 연속적 분포를 가졌고 HCM방식으로 증착한 titanium박막의 in-plane grain size가 다른 증착방식으로 증착한 박막에 비해 크게 관찰됨을 Plan-view TEM 분석을 통해서 확인되었다.

• Journal of Electrochemical Science and Technology
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• v.15 no.1
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• pp.51-66
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• 2024

Modern society is making numerous efforts to reduce reliance on carbon-based energy systems. A notable solution in this transition is the adoption of lithium-ion batteries (LIBs) as potent energy sources, owing to their high energy and power densities. Driven by growing environmental challenges, the application scope of LIBs has expanded from their initial prevalence in portable electronic devices to include electric vehicles (EVs) and energy storage systems (ESSs). Accordingly, LIBs must exhibit long-lasting cyclability and high energy storage capacities to facilitate prolonged device usage, thereby offering a potential alternative to conventional sources like fossil fuels. Enhancing the durability of LIBs hinges on a comprehensive understanding of the reasons behind their performance decline. Therefore, comprehending the degradation mechanism, which includes detrimental chemical and mechanical phenomena in the components of LIBs, is an essential step in resolving cycle life issues. The LIB systems presently being commercialized and developed predominantly employ graphite anode and layered oxide cathode materials. A significant portion of the degradation process in LIB systems takes place during the electrochemical reactions involving these electrodes. In this review, we explore and organize the aging mechanisms of LIBs, especially those with graphite anodes and layered oxide cathodes.

• Environmental Engineering Research
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• v.19 no.4
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• pp.363-367
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• 2014

One chambered sediment microbial fuel cell (SMFC) was equipped with Fe, brass (Cu/Zn), Fe/Zn, Cu, Cu/carbon cloth and graphite felt anode. Graphite felt was used as common cathode. The SMFC was membrane-less and mediator-less as well. Order of anodic performance on the basis of power density was Fe/Zn ($6.90Wm^{-2}$) > Fe ($6.03Wm^{-2}$) > Cu/carbon cloth ($2.13Wm^{-2}$) > Cu ($1.13Wm^{-2}$) > brass ($Cu/Zn=0.24Wm^{-2}$) > graphite felt ($0.10Wm^{-2}$). Fe/Zn composite anode have twisted 6.73% more power than Fe alone, Cu/carbon cloth boosted power production by 65%, and brass (Cu/Zn) produced 65% less power than Cu alone. Graphite felt have shown the lowest electricity generation because of its poor galvanic potential. The estuarine sediment served as supplier of oxidants or electron producing microbial flora, which evoked electrons via a complicated direct microbial electron transfer mechanism or making biofilm, respectively. Oxidation reduction was kept to be stationary over time except at the very initial period (mostly for sediment positioning) at anodes. Based on these findings, cost effective and efficient anodic material can be suggested for better SMFC configurations and stimulate towards practical value and application.

• Journal of Power Electronics
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• v.7 no.1
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• pp.38-43
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• 2007

An External Electrode Fluorescent Lamp (EEFL) has longer lifespan, higher power efficiency and higher luminance than a Cold Cathode Fluorescent Lamp (CCFL). Moreover, it is easy to drive them in parallel. Therefore, the EEFL is expected to quickly replace the CCFL in LCD backlight systems. However, the EEFL has more complex characteristics than the CCFL with a resistive component, because it has both a resistive component by plasma and a capacitive component by external electrode. In this paper, values of resistance and capacitance are measured at several power levels and at several operating frequencies. They are expressed by a numeral formula based on a linear approximation that represents the equivalent resistance and capacitance as a function of power. Then we made block diagram of the equivalent circuit model using numerical expressions. Simulation waveforms and experimental results are presented to verify the feasibility of the equivalent model.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.1
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• pp.77-82
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• 2011

In this study, a metal-supported SOFC was fabricated using a relatively cheap and simple process. The adhesion process between ceramic cell and metal support was performed in high temperature over $1400^{\circ}C$ and the deformation of large metal-supported cell happened in this process. Using bi-layered metal support fabricated by diffusion bonding, the deformation of the metal-supported cell can be minimized and the sealing efficiency of anode and cathode was improved. The flatness of the cell was improved by over 20% and the maximum power density of over 0.5 $Wcm^{-2}$ was obtained at the operation condition of $800^{\circ}C$.