• Applied Chemistry for Engineering
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• v.31 no.5
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• pp.509-513
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• 2020

The performance of TiO₂ microcones/CNT composites as an anode material for lithium ion batteries was investigated. TiO₂ microcones/CNT composites were prepared by the polarization followed by electrophoretic deposition approaches on anodic TiO₂ microcones, which were composed of individual nanofragments resulting in a large surface area where lithium ion can be stored. Compared to pristine TiO₂ microcones, TiO₂ microcones/CNT composite electrodes showed higher areal capacity with a stable cyclability due to an enhanced electrical and lithium ion conductivity. Furthermore, TiO₂ microcones/CNT composite electrodes exhibited good cycle life characteristics and excellent rate retention under a high current density of up to 20 C.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1424-1426
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• 1997

저전압 구동이 가능한 교류구동형 박막전기발광소자를 구현하기 위해 높은 유전상수를 가지며 특히 광학적 굴절률이 발광박막과 유사하여 광학적 특성 개선에도 효과적인 것으로 알려져 있는 $Ta_2O_5$를 제조하였다. $Ta_2O_5$박막은 rf-magnetron sputtering방법으로 형성하였으며 기판온도, working pressure, 박막의 두께에 따른 전기적인 특성을 조사하였다. 10mTorr에서 제조된 $Ta_2O_5$박막은 $22{\sim}26$의 비유전율을 보였고, 유전손실은 $0.007{\sim}0.03(1kHz{\sim}10kHz)$의 값을 보였다. $100^{\circ}C$에서 제조된 박막의 전하저장용량은 $7.9{\mu}C/cm^2$이었다. 제조된 박막의 항복전압은 인가 전압의 극성에 의존하며, 전류특성은 기판온도와 200nm와 300nm의 두께에서는 $V^{1.95}{\sim}V^{2.35}$에 비례하는 space charge limited current특성을 보였고, 400nm에서는 Poole Frenkel특성을 보였다. 이상의 결과로 TFEL소자에 응용에 적합한 $Ta_2O_3$ 박막은 $200^{\circ}C$에서 증착되고 200nm와 300nm인 것으로 나타났으며, 제조된 MIS구조(ITO-$Ta_2O_5$-ZnS-Al)의 ACTFEL소자에서의 전도전하는 각각 $13uC/cm^2$, $8.3uC/cm^2$로 조사되었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.6
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• pp.427-434
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• 2013

In this paper, the design and layout of a 2.5 Gbps arrayed VCSEL driver for optical transceiver having arrayed multi-channel of integrating module is confirmed. In this paper, a 4 channel 2.5 Gbps VCSEL (vertical cavity surface emitting laser) driver array with automatic optical power control is implemented using $0.18{\mu}m$ CMOS process technology that drives a $1550{\mu}m$ high speed VCSEL used in optical transceiver. To enhance the bandwidth of the optical transmitter, active feedback amplifier with negative capacitance compensation is exploited. We report a distinct improvement in bandwidth, voltage gain and operation stability at 2.5Gbps data rate in comparison with existing topology. The 4-CH chip consumes only 140 mW of DC power at a single 1.8V supply under the maximum modulation and bias currents, and occupies the die area of $850{\mu}m{\times}1,690{\mu}m$ excluding bonding pads.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.1
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• pp.27-31
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• 2007

The cpapcitors with MIM(metal-insulator-metal) structures using PVP gate insulation films were prepared for the application of flexible organic thin film transistors (OTFT). The co-polymer organic insulation films were synthesized by using PVP(poly-4-vinylphenol) as a solute and PGMEA(propylene glycol monomethyl ether acetate) as a solvent. The cross-linked PVP insulation films were also prepared by addition of poly(melamine-co-formaldehyde) as thermal hardener. The leakage current of the cross- linked PVP films was found to be about 1.3 nA on Al/PES(polyethersulfone) substrate, whereas, on ITO/ glass substrate was about 27.5 nA indicating improvement of the leakage current at Al/PES substrates. Also, the capacitances of all prepared samples on ITO/glass and Al/PES substrates w ere ranged from 1.0 to $1.2nF/cm^2$, showing very similar result with the calculated capacitance values.

• Journal of the Korean Electrochemical Society
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• v.8 no.2
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• pp.77-81
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• 2005

Porous-composite electrodes have been developed using silica gel, which reduce carbon aerogel usage with high cost. Silica gel powder was added to the carbon aerogel to simplify the manufacturing procedure and to increase the wet-ability, the mechanical strength and the CDI efficiency. Porous composite electrodes composed of carbon aerogel and silica gel powder were prepared by paste rolling method. Carbon aerosol composite electrodes with $10\times10cm^2$ are placed face to face between spacers, and assembled the four-stage series cells for CDI process. Each stage is composed of 45 cells. Four-stage series cells (flow through cells) for CDI process are put in continuous-system reactor containing 1,000ml-NaCl solution bath of 1,000 ppm. The four-stage series cells with carbon aerogel electrodes are charged at 1.2V and are discharged at 0.001V, and then read the current. Conclusively, removal efficiencies of ions using the four-stage series cells composed of carbon aerogel composite electrodes show good removal efficiency of $99\%$ respectively.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.157-161
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• 2013

Porous $LiMn_{0.6}Fe_{0.4}PO_4$ (LMFP) was synthesized by a sol-gel process. Uniform dispersion of the conductive carbon source throughout LMFP with uniform carbon coating was achieved by heating a stoichiometric mixture of raw materials at $600^{\circ}C$ for 10 h. The crystal structure of LMFP was investigated by Rietveld refinement. The surface structure and pore properties were investigated by SEM, TEM and BET. The LMFP so obtained has a high specific surface area with a uniform, porous, and web-like nano-sized carbon layer at the surface. The initial discharge capacity and energy density were 152 mAh/g and 570 Wh/kg, respectively, at 0.1 C current density, and showed stable cycle performance. The combined effect of high porosity and uniform carbon coating leads to fast lithium ion diffusion and enhanced electrochemical performance.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.8
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• pp.109-115
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• 2008

A design criterion of grounding systems is commonly based on the ground resistance measured with low frequency in Korea. When lightning surges which have high frequency components are injected into the grounding system, the grounding impedance is great]y different from the static grounding resistance. In order to investigate the effect of water resistivity on the high frequency performance of grounding systems, this paper presents the frequency-dependent admittance using water tank simulating the grounding system in different water resistivities. As a result, because of capacitive effect admittances and conductance are increased with increasing frequency in higher water resistivity of greater than 500[${\Omega}{\cdot}m$]. On the other hand, admittances and conductances are decreased with increasing frequency due to inductive effect in lower water resistivity of less than 500[${\Omega}{\cdot}m$]. The phase difference between the current and voltage increases in the range of 200[kHz] to 5[MHz]. Consequently, frequency-dependent performance of grounding systems is closely related to the soil resistivity, it is necessary to consider the effect of grounding system performance on the frequency and soil resistivity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.4
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• pp.664-669
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• 2018

To observe the relationship between the oxygen vacancy and electrical characteristics of $TiO_2$ due to the $CO_2$ gases, the $TiO_2$ were deposited by the mixing gases of $Ar:O_2=20$ sccm:20 sccm and annealed with various temperatures. The bonding structure was changed with the annealing temperature from amorphous to crystal structure, and the oxygen vacancy was also changed with these bonding structures. The $CO_2$ gas reaction of $TiO_2$ films showed the variation in accordance with the bonding structure. The capacitance increased at the amorphous structure $TiO_2$, and the current also increased. However the oxygen vacancy decreased at this amorphous structure $TiO_2$. Because of the formation of oxygen vacancies is in inverse proportion to the amorphous structure. Moreover, the diffusion current in the depletion layer such as the amorphous structure showed the difference in accordance with the $CO_2$ gas flow rates.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.1
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• pp.62-71
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• 2009

In this paper, an improved drive method of piezoelectric PZT stack actuator for micro-positioning system is proposed and the performances are evaluated. This type of amplifier is based on switching technology efficiently handling the arbitrary regenerative energy from the piezoelectric actuator. The conventional voltage-feedback control method has the THD of -32dB (${\approx}2.5%$) with 100mHz sinusoidal reference, which means that the positioning performance in linearity degrades due to the hysteretic relationship between actuator voltage and the displacement. This paper proposed an improved charge-controlling method, which utilizes differential information of charge reference instead of integrating the actuator's current. The current waveform has THD under -40dBV (=1%) and the displacement waveform nearly -52dB (${\approx}0.25%$), which means that the positioning performance is very excellent. Finally, another method of the displacement feedback control has better performance than the voltage method, however there exists a limitation in performance of the system.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.5
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• pp.372-378
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• 2009

With the increase in capacity of photovoltaic generation systems, studies are being actively conducted to improve system efficiency. In order to develop the high performance photovoltaic power system it is required to understand the physical characteristics of the solar cell. However, solar cell models have a non-linear form with many parameters entangled and conventional methods suggested to extract the parameters of the solar cell model require some kind of assumptions, which accompanies the calculation errors, thereby lowering the accuracy of the model. Therefore, in this paper a novel method is proposed to calculate the ideality factor and reverse saturation current of the solar cell from the I-V curve measured and announced by solar cell manufacturers, derive the ideal I-V curve, and then extract the series and shunt resistances value from the difference between the ideal and measured I-V curve. Also, validity of the proposed method is demonstrated by calculating the correlation between I-V curve based on modeling parameters and I-V curve actually measured through least squares method.