• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.12
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• pp.11-20
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• 1999

We have designed and fabricated direct-and gap-coupled microstrip hairpin-comb filters by patterning double-sided YBCO films on a single 50-mm-diameter, 0.5-mm-thick $LaAlO_3$ wafer. Both filters have a center frequency at 1.773 GHz, 12 MHz bandwidth, 0.5 dB minimum insertion loss in the passband, and very strong out-of- band rejection. Due to two attenuation poles below and above the passband, the direct-coupled hairpin-comb filter showed a better skirt characteristic than the gapcoupled hairpin-comb filter which had only one attenuation pole below the passband.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.3
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• pp.558-564
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• 2012

We fabricated Ga doped ZnO (GZO) thin films on the glass substrate (Eagle 2000) with various of Ga doping concentration and annealing temperatures using sol-gel method, electrical and optical properties were investigated. When the GZO thin films doped with 1 mol% of Ga and annealed at $600^{\circ}C$, the excellent (002) orientation was observed. In the results of Hall measurement, carrier concentration decreased and resistivity increased due to segregation effect with increasing of the Ga doping concentration. The largest carrier concentration and lowest resistivity were $9.13{\times}10^{18}cm^{-3}$ and $0.87{\Omega}cm$, respectively, in the GZO thin films doped with 1 mol% Ga and annealed at $600^{\circ}C$. All films is higher than 80 % in the visible light region. Energy band gap narrowing due to Burstein-Moss effect was observed with increasing of Ga doping concentration from 1 to 4 mol%.

• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.571-575
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• 2017

In this study, cadmium telluride (CdTe) quantum dots were synthesized by using ultrasonic irradiation method. Optical properties and structural characteristics of the CdTe quantum dots were analyzed by two main variables; the ratio of the precursor and the synthesis time. As the synthesis time increased, the band gap reduction was observed with the growth of CdTe quantum dots. As for the luminescence properties, the red shift appeared at 510~610 nm wavelength range. Also, it was confirmed that the red shift occurs rapidly as the ratio of Te increases. According to PL peak intensity, the highest intensity was shown at 180 to 240 min. Structural characteristics of CdTe quantum dots were investigated through XRD and TEM, and the cubic zinc blend structure was observed. The size of quantum dots was about 2.5 nm and uniformly dispersed when the synthesis time took 210 min. In addition, the apparent crystallinity was discovered in FFT image.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.27-28
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• 2014

투명전극이란 전기 전도도를 갖는 동시에 가시광선 영역에서 빛을 투과하는 성질을 가지는 소재이다. 일반적으로 가시광선 영역(380nm~780nm)에서 80%이상의 광 투과도를 가지며, 비저항이 $10^{-3}{\Omega}{\cdot}cm$ 이하, optical band gap 이 3.3 eV 이상인 물질을 TCO(Transparent Conducting oxide)라고 한다. 현재까지 국내의 TCO 관련 연구는 터치패널, 디스플레이, 태양전지 등 광전자분야에서 가장 널리 사용되고 있는 ITO(Sn:In2O3)에 치중되어 있으며, 관련 연구도 거의 디스플레이 맞춤형 연구개발이 주류를 이루어왔다. ITO가 전기전도성이 우수하고 동시에 가시광선 영역에서의 투과율도 80%이상으로 전기적, 광학적 특성이 우수하다는 장점을 가지고 있으나, In의 희소성으로 인한 고가격, 유독성, 접착력 문제 때문에 이를 대체하기 위해 제조원가가 ITO에 비하여 월등히 저렴하고 내화학성과 내마모성이 우수하면서도, 가시광선 영역에서의 광투과율이 80%이상으로 좋다는 $SnO_2$에 관한 연구가 활발히 진행되어 왔다. 적절한 dopant를 첨가하여 $SnO_2$자체의 높은 광학적 투과도를 유지하면서 전기전도성을 더 높일수 있고, 투명전극이 가져야 할 고온 안정성을 가지고 있으며 비독성이고 수소 플라즈마에 대한 내성이 더 클 뿐만 아니라 저온에서 성장이 가능하다. $SnO_2$의 전기 전도도를 높이기 위한 Al, In, Ga, B와 같은 3족 원소가 $SnO_2$의 n형 dopant로 널리 사용되고 있다. 그 중 Al은 반응성이 커서 박막 증착 중에 산화되기 쉬운 반면, 전기적 특성 및 광학적 특성의 향상을 이룰 수 있다. 본 연구에서는 Rf Sputtering법을 사용하여 quartz기판 위에 다층박막 형태의 투명전도막을 제작한 후, 열처리를 수행, 이에 의한 다층박막 내 계면간 상호확산 현상을 이용하여 투명 전도막의 특성변화를 관찰하였다. 박막의 구조적 특성은 XRD장비를 사용하여 분석하였으며, 전기적, 광학적 특성은 각각 표면저항기, 홀 측정 장비, 그리고 UV-VIS-NI를 사용하여 확인하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.264-265
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• 2014

This Paper reports the photocatalytic activity of $g-C_3N_4/NaTaO_3$ hybrid composite photocatalysts synthesized by ball-mill method. The $g-C_3N_4$ and $NaTaO_3$ were individually prepared by Solid state reaction and microwave hydrothermal process, respectively. The $g-C_3N_4/NaTaO_3$ composite showed the enhanced photocatalytic activity for degradation of rhodamine B dye (Rh. B) under simulated solar light irradiation. The results revealed that the band-gap energy absorption edge of hybrid composite samples was shifted to a longer wavelength as compared to $NaTaO_3$ and the 50 wt% $g-C_3N_4/NaTaO_3$ hybrid composite exhibited the highest percentage (99.6 %) of degradation of Rh. B and the highest reaction rate constant ($0.013min^{-1}$) in 4 h which could be attributed to the enhanced absorption of the hybrid composite photocatalyst in the UV-Vis region. Hence, these results suggest that the $g-C_3N_4/NaTaO_3$ hybrid composite exhibits enhanced photocatalytic activity for the degradation of rhodamine B under simulated solar light irradiation in comparison to the commercial $NaTaO_3$.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.57-61
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• 2004

Zinc Oxide (ZnO) have the crystal structure of wurtzite which is semiconducting oxide with band gap energy of 3.3eV. $In_2O_3$-doped ZnO films were fabricated by electron beam evaporation at $400^{\circ}C$ and their characteristics were investigated. The content of $In_2O_3$ in ZnO films had a marked effect on the electrical properties of the films. As $In_2O_3$ content decreased. $In_2O_3$-doped ZnO films was converted amorphous into crystallized films and showed a better characteristics generally as a transparent conducting oxide. As $In_2O_3$-doped ZnO films were prepared by $In_2O_3$-doped ZnO pellet with 0.2at% of $In_2O_3$ content, the value of resistivity was about $6.0 {\times} 10^{-3} {\Omega}cm$. The transmittance was higher than 85% throughout the visible range.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.10
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• pp.1054-1060
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• 2002

In this paper, a new parallel-coupled-line microstrip BPF(BandPass Filter) improving the suppression performance of 2nd harmonic signals is studied. Using the consecutive pattern in coupled-line, the desired passband performance is improved and harmonic passband signal is rejected. Recalculation of classical filter design parameters(space-gap between lines, line widths and lengths) is not required. That is, after using the classical design methodology for parellel-coupled-line BPF, new filters can be easily realized by inserting periodic patterns in coupled-line. To investigate the validity of this novel technique, order-3 Butterworth BPF centered at 2.5 GHz with a 10 % FBW(Fractional Bandwidth) and order-5 Chebyshev BPF centered at 10 GHz with a 15 % FBW were used. When five and three square grooves are used, over 30 dB harmonic suppression at 2nd harmonic is achieved in simulation and experiment.

• Corrosion Science and Technology
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• v.2 no.2
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• pp.68-74
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• 2003

The effects of Niobium on the structure and properties(especially electric properties) of passive film of Zirconium alloys in pH 8.5 buffer solution are examined by the photo-electrochemical analysis. For Zr-xNb alloys (x = 0, 0.45, 1.5, 2.5 wt%), photocurrent began to increase at the incident energy of 3.5 ~ 3.7 eV and exhibited the $1^{st}$ peak at 4.3 eV and the $2^{nd}$ peak at 5.7 eV. From $(i_{ph}hv)^{1/2}$ vs. hv plot, indirect band gap energies $E_g{^1}$= 3.01~3.47 eV, $E_g{^2}$= 4.44~4.91 eV were obtained. With increasing Nb content, the relative photocurrent intensity of $1^{st}$ peak significantly increased. Compared with photocurrent spectrum of thermal oxide of Zr-2.5Nb, It was revealed that $1^{st}$ peak in photocurrent spectrum for the passive film formed on Zr-Nb alloy was generated by two types of electron transitions; the one caused by hydrous $ZrO_2$ and the other created by Nb. Two electron transition sources were overlapped over the same range of incident photon energy. In the photocurrent spectrum for passive film formed on Zr-2.5Nb alloy in which Nb is dissolved into matrix by quenching, the relative photocurrent intensity of $1^{st}$ peak increased, which implies that dissolved Nb act as another electron transition source.

• Journal of IKEEE
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• v.14 no.2
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• pp.90-97
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• 2010

The high efficiency power management IC(PMIC) with DTMOS(Dynamic Threshold voltage MOSFET) switching device and DTMOS Error Amplifier is presented in this paper. PMIC is controlled with PWM control method in order to have high power efficiency at high current level. Dynamic Threshold voltage CMOS(DT-CMOS) with low on-resistance is designed to decrease conduction loss. The control parts in Buck converter, that is, PWM control circuits consist of a saw-tooth generator, a band-gap reference circuit, an DT-CMOS error amplifier and a comparator circuit as a block. the proposed DT-CMOS Error Amplifier has 72dB DC gain and 83.5deg phase margin. also Error Amplifier that use DTMOS more than CMOS showed power consumption decrease of about 30%. DC-DC converter, based on Voltage-mode PWM control circuits and low on-resistance switching device is achieved the high efficiency near 96% at 100mA output current. And DC-DC converter is designed with Low Drop Out regulator(LDO regulator) in stand-by mode which fewer than 1mA for high efficiency.

• Journal of IKEEE
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• v.21 no.1
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• pp.73-76
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• 2017

SiC devices have drawn much attentions for its wide band gap material properties. Especially 4H-SiC Schottky barrier diode is widely used for its rapid switching speed and low forward voltage drop. However, the low reliability of Schottky barrier diode has many problems that Super Barrier Rectifier(SBR) was researched for alternative. makes 4H-SiC trench-type accumulation super barrier rectifier(TASBR) is analyzed and proposed in this paper. We could verified that forward voltage drop was improved 21.06% without severe degradation of reverse breakdown voltage and leakage current based on the results from 2-D numerical simulations. With this novel rectifier structure, we can expect application with less power loss.