• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.12
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• pp.769-776
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• 2016

In this study, a numerical simulation of a vanadium redox flow battery was investigated for reactions involving an electrochemical species using comprehensive conservation laws and a kinetic model. For a 3-D geometry of the cell, the distributions of electric potential, vanadium concentration, overpotential, and ohmic loss were calculated. The cell temperature and initial vanadium ion concentration were set as variables. The voltage and electrochemical loss were calculated for each variable. The effects of each variable's impact on the electrochemical performance of a vanadium redox flow battery was numerically analyzed using the calculated overpotential in the electrode and the ohmic loss in the electrolyte phase. The cell temperature increased from $20^{\circ}C$ to $80^{\circ}C$ when the voltage efficiency decreased from 89.34% to 87.29%. The voltage efficiency increased from 88.65% to 89.25% when the vanadium concentration was changed from $1500mol/m^3$ to $3000mol/m^3$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.8
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• pp.687-693
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• 2014

In this study, the performance characteristics of a polymer electrolyte membrane fuel cell (PEMFC) were investigated at low operating temperatures under steady-state and dynamic conditions. The performance of the PEMFC was analyzed according to the external humidifying rate and air stoichiometry. The ohmic resistance was also investigated using EIS tests. At the operating temperature of $35^{\circ}C$, voltage fluctuation occurred to a greater degree compared to that at $45^{\circ}C$. Therefore, it was found that the air stoichiometry should be higher than 2.5 for the stable operation of the fuel cell. In addition, the relative humidity of the reactant gases should be higher than 60 to reduce the ohmic resistance.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.1
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• pp.59-68
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• 2009

Fuel cell generators as the distributed generation system with a few hundred watt$\sim$a few hundred kilowatt capacity, can supply the high quality electric power to user as compared with conventional large scale power plants. In this paper, PEMFC(polymer electrolyte membrane fuel cell) generator as micro-source is modelled by using PSIM simulation software and DSP based fuel cell hardware simulator based on the PSIM simulation model is implemented. The relation of fuel cell voltage and current(V-I curve) is linearized by first order function on the ohmic area in voltage-current curve of fuel cell. The implemented system is composed of a PEMFC hardware simulator, an isolated full bridge dc boost converter, and a 60[Hz] voltage source PWM inverter. The voltage-current-power(V-I-P) characteristics of the implemented fuel cell hardware simulator are verified in load variation and transient state and the 60[Hz] output voltage sinusoidal waveform of the PWM inverter is investigated under the resistance load and nonlinear diode load.

• Journal of the Korean Vacuum Society
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• v.11 no.1
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• pp.35-42
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• 2002

We fabricate thermally stable and low resistance Ru ohmic contacts to $n-ZnO:Al(3\times10^{18}\textrm{cm}^{-3})$, grown by specially designed dual target sputtering system. It is shown that the as-deposited Ru contact produces a specific contact resistance of $2.1{\times}10^{-3}{\Omega}\textrm{cm}^2$. Annealing of the Ru contacts leads to the improvement of current-voltage characteristics. For example, annealing of the contact at $700^{\circ}C$ for 1 min produces a contact resistance of $3.2{\times}10^{-5}}{\Omega}\textrm{cm}^2$. furthermore, the metallisation scheme is found to be thermally stable: the surface of the contact is fairly smooth with a rms roughness of 1.4 nm upon annealing at $700^{\circ}C$. These results strongly indicate that the Ru contact represents a suitable metallisation scheme for fabrication of high-performance ZnO-based optical devices and high-temperature devices. In addition, possible mechanisms are suggested to describe the annealing temperature dependence of the specific contact resistance.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.7
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• pp.66-79
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• 1999

We investigate the effects of high input power on the performance of optical bistable symmetric self-electooptic effect devices (S-SEEDs) using extremely shallow quantum wells (ESQWs). In this study, we consider the four ESQWs SEEDs; anti-reflection (AR)-coated ESQWs S-SEED, back-to-back AR coated ESQWs S-SEED, asymmetric F뮤교-Perot (AFP) ESQWs S-SEED, and back-to-back AFP-ESQWs S-SEED. As the input power increases, device performances such as on/off contrast ratio, on/off reflectivity difference are seriously degraded because of ohmic heating and exciton saturation. On the other hand, switching speed of the device increases up to certain value and then begins to decrease. With reasonable optimization of the input power for the best switching speed operation of the devices in a cascading optical interconnection system, we simulate and analyze the system bit-rate of the various ESQWs S-SEEDs, for a mesa of $5{\times}5{\mu}m^2$ size, changing the namber of quantum wells for the external bias of 0 V and -5V.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.2
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• pp.33-37
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• 2014

We have developed a novel passivation process employing a sacrificial gallium oxide process in order to recover the surface damage in AlGaN/GaN HFETs. Even with a conventional prepassivation process, surface damage during high temperature ohmic annealing cannot be avoided completely. Therefore, it is necessary to recover the damaged surface to avoid the characteristic degradation. In this work, a sacrificial gallium oxide process has been proposed in which the damaged surface after ohmic annealing was oxidized by oxygen plasma treatment and thereafter etched back using HCl. As a result, the leakage current was dramatically reduced and thus the subthreshold slope was significantly improved. In addition, the maximum drain current level was increased from 594 to 634 mA/mm. To verify the effects, the surface conditions were carefully investigated using X-ray photoelectron spectroscopy.

• ETRI Journal
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• v.24 no.5
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• pp.349-359
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• 2002

With Ni/Au and Pd/Au metal schemes and low temperature processing, we formed low resistance stable Ohmic contacts to p-type GaN. Our investigation was preceded by conventional cleaning, followed by treatment in boiling $HNO_3$:HCl (1:3). Metallization was by thermally evaporating 30 nm Ni/15 nm Au or 25 nm Pd/15 nm Au. After heat treatment in $O_2$ + $N_2$ at various temperatures, the contacts were subsequently cooled in liquid nitrogen. Cryogenic cooling following heat treatment at $600^{\circ}C$ decreased the specific contact resistance from $9.84{\times}10^{-4}$ ${\Omega}cm^2$ to $2.65{\times}10^{-4}$ ${\Omega}cm^2$ for the Ni/Au contacts, while this increased it from $1.80{\times}10^{-4}$ ${\Omega}cm^2$ to $3.34{\times}10^{-4}$ ${\Omega}cm^2$ for the Pd/Au contacts. The Ni/Au contacts showed slightly higher specific contact resistance than the Pd/Au contacts, although they were more stable than the Pd contacts. X-ray photoelectron spectroscopy depth profiling showed the Ni contacts to be NiO followed by Au at the interface for the Ni/Au contacts, whereas the Pd/Au contacts exhibited a Pd:Au solid solution. The contacts quenched in liquid nitrogen following sintering were much more uniform under atomic force microscopy examination and gave a 3 times lower contact resistance with the Ni/Au design. Current-voltage-temperature analysis revealed that conduction was predominantly by thermionic field emission.

• Journal of Sensor Science and Technology
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• v.26 no.6
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• pp.438-444
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• 2017

In this paper, we focus on optimization of the in-situ phosphorous (P) doping of low-pressure chemical vapor deposited (LPCVD) poly Si resistors for obtaining near-zero temperature coefficient of resistance (TCR) at temperature range from 25 to $600^{\circ}C$. The deposited poly Si films were annealed by rapid thermal anneal (RTA) process at the temperature range from 900 to $1000^{\circ}C$ for 90s in nitrogen ambient to relieve intrinsic stress and decrease the TCR in the poly Si layer and get the Ohmic contact. After the RTA process, a roughness of the thin film was slightly changed but the grain size and crystallinity of the thin film with the increase in anneal temperature. The film annealed at $1,000^{\circ}C$ showed the behavior of Schottky contact and had dislocations in the films. Ohmic contact and TCR of $334.4{\pm}8.2$ (ppm/K) within 4 inch wafer were obtained in the measuring temperature range of 25 to $600^{\circ}C$ for the optimized 200 nm thick-poly Si film with width/length of $20{\mu}m/1,800{\mu}m$. This shows the potential of in-situ P doped LPCVD poly Si as a resistor for pressure sensor in harsh environment applications.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.91-91
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• 1999

광소자 기술은 정보 전달 및 저장 기술의 지속적인 증가 요구에 따라 발전을 거듭하여 왔다. 특히 광통신 및 저장 기술에서 광원으로 사용되는 레이저 다이오드는 안정되면서 쉽게 제작할 수 있어야 한다. 이온 주입 방법은 반도체 공정에서 광범위하게 사용되는 공정이며 이미 소자측면에서 안정성이 확보되었다고 볼 수 있으나 대부분 메모리 등의 실리콘 반도체에서 이용되어 왔다. 최근에는 화합물 반도체 분야에서도 적용하는 예가 증가되고 있으나 광원으로 사용되는 레이저 다이오드의 경우는 우수한 품질의 반도체 층이 요구되며 따라서 damage가 큰 이온 주입 방법을 이용한 연구는 아직 많이 이루어져 있지 않다. 본 연구에서는 레이저 다이오드 구조의 성장측에 국부적으로 Fe 이온을 주입하여 도파로를 형성하여 광을 구속하여 도파시키는 동시에 전기적으로도 도파로 부분으로만 다이오드가 형성되도록 하고자 한다. 먼저 p층의 전기적 절연에 필요한 조건을 확보하기 위하여 CBE를 사용하여 Fe가 doping 된 SI-InP wafer 위에 p-InP (Be:5x1017 cm-3)층을 1.2$mu extrm{m}$ 성장한 후 ohmic 층으로 p-InGaAs (Be:1x1019 cm-3)을 0.1$\mu\textrm{m}$ 성장한 시료에 고에너지 이온 주입 장치를 사용하여 Fe 이온을 1MeV, 1.6meV의 에너지에 각각 1x1014cm-2, 2x1014cm-2 의 dose로 전면에 implant 하였다. 이 시료를 tube furnace에서 500, 600, $700^{\circ}C$각각 10분씩 annealing 한 후 재성장을 확인하기 위하여 DCXRD을 측정하였다. 그림 1은 DCXRD rocking curve로 annealing 하기 전 후의 In rich에서 side peak의 감소를 확인 할 수 있었는데 이는 damage가 어느 정도 복구되었음을 의미한다. 또한 절연 특성을 확인하기 위하여 ohmic metal을 증착하여 Hall 효과를 측정하였다. 그림 2에 보이는 것과 같이 annealing 온도가 증가함에 따라 면저항이 크게 증가함을 볼 수 있으며 이온 주입하기 전의 시료에 비해 104 이상의 저항을 갖을 수 있다. 향후 이러한 결과를 바탕으로 1.55$\mu\textrm{m}$ LD 구조에서 발진 특성을 관찰할 계획이다.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.2 s.39
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• pp.15-19
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• 2006

The resistance switching characteristics of amorphous $SiO_2$ and poly-crystalline $TiO_2$ were investigated. Both films exhibit well defined switching characteristics with low and high resistance states. From I-V curve analyses, it was found that the low resistance states of both films obey an ohmic conduction mechanism and the high resistance states show generation of a Schottky potential barrier. Regarding the mechanism for resistance switching of the binary oxide, it is suggested that the generation and annihilation of potential barriers accounts for the changes to the high resistance state and low resistance state, respectively. The device operation characteristic parameters such as reset and set voltages of $TiO_2$ are distinctly smaller than those of $SiO_2$, indicating that the values are related to the dielectric constant.