• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제9권4호
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• pp.473-482
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• 1998

In this paper, characteristics of the wide band microstrip antennas with parasistic element are analyzed by the Finite Difference Time Domain(FDTD) method, and antenna parameters are optimized to get maximum bandwidth, retern loss, input impedance, and radiation pattern are calculated by Founier transforming the time domain results. The characteristics of the antenna are varied and the bandwidth of the antenna is broaded as a length and a width of the driven element, a gap of the driven element and the parasitic element, a width and a length of parasitic element. So the different patchs are resonating at different frequencies and this multipule resonance increase the bandwidth. The Results of the calculation and measurement, the size of the antenna with parasitic element is about a twice larger than a microstrip antenna, but bandwidth is four times better than a microstrip antenna. And these results were in relatively good accordance with the measured values.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2849-2853
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• 2010

A method to improve the photocatalytic activity of titanium dioxide by modification with a sensitizer and a metal oxide is proposed. To achieve this goal, we used metal oxides as dopants. In particular, $CaWO_4$ and $Gd_2O_2S$:Tb were used because their 2.6 eV and 2.2 eV band gap energy and optical properties have a large positive effect on photocatalysis. The improvement in the photocatalytic activity of $TiO_2$ modified with $Gd_2O_2S$:Tb under ultraviolet light irradiation is described in a previous study. The present work focuses on the sensitization of metal oxide-modified $TiO_2$. Having observed the ultraviolet-visible absorption spectra of 3,4,9,10-Perylenetetracarboxylic diimide in the wide visible-light region from 400 nm to 650 nm and the broad peaks in its photoluminescence spectra at 695 nm and 717 nm, we decided to use this perylene dye to sensitize modified $TiO_2$ to enhance its activity as a visible-light harvesting photocatalyst. We also explored the positive effects thin-film surface changes stemming from ultraviolet pre-treatment have on photocatalytic activity. Finally, we subjected several metal oxide-modified $TiO_2$ products sensitized by the perylene dye to ultraviolet pre-treatment, obtaining the most active photocatalysts.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제42권12호
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• pp.171-176
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• 2005

This study designed and fabricated a multi-purpose planar antenna for base stations that are accessible to DCS, WiBro, and ISM. The proposed antenna was designed into an open loop form from the existing monopole structure. The capacitance of the multi-purpose antenna was increased by the coupling of open parts. This makes the use of MMIC and LTCC convenient and the antenna is smaller and has a larger gain than existing antennas. The resonance distance and bandwidth can be adjusted by changing the open gap and the height of the loop of the antenna. The bandwidth of the designed antenna satisfies DCS, IMT-2000, WiBro, Bluetooth, wireless LAN and ISM bands based on VSWR 2. The entire frequency bandwidth is $58.75\%$ of $1.575GHz\~2.985GHz(1.41GHz)$. Also, the radiation pattern of the antenna displayed co-polarization and cross-polarization characteristics at 1.6GHz, 2.3GHz and 2.8GHz.

• Journal of IKEEE
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• 제21권1호
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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.

• Proceedings of the Materials Research Society of Korea Conference
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• 한국재료학회 2009년도 춘계학술발표대회
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• pp.24.1-24.1
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• 2009

The zinc oxide (ZnO) material as the II-VI compound semiconductor is useful in various fields of device applications such as light-emitting diodes (LEDs), solar cells and gas sensors due to its wide direct band gap of 3.37eV and high exciton binding energy of 60meV at room temperature. In this study, the ZnO nanorods were deposited onto homogenous buffer layer/Si(100) substrates by a hydrothermal synthesis. The Effects of the buffer layer annealing and post annealing temperature on the structural and optical properties of ZnO nanorods grown by a hydrothermal synthesis were investigated. For the buffer layer annealing case, the annealed buffer layer surface became rougher with increasing of annealing temperature up to $750^{\circ}C$, while it was smoothed with more increasing of annealing temperature due to the evaporation of buffer layer. It was found that the roughest surface of buffer layer improved the structural and optical properties of ZnO nanorods. For the post annealing case, the hydrothermally grown ZnO nanorods were annealed with various temperatures ranging from 450 to $900^{\circ}C$. Similarly in the buffer layer annealing case, the post annealing enhanced the properties of ZnO nanorods with increasing of annealing temperature up to $750^{\circ}C$. However, it was degraded with further increasing of annealing temperature due to the violent movement of atoms and evaporation. Finally, the buffer layer annealing and post annealing treatment could efficiently improve the properties of hydrothermally grown ZnO nanorods. The morphology and structural properties of ZnO nanorods grown by the hydrothermal synthesis were measured by atomic force microscopy (AFM), field emission scanning electron microscopy (SEM), and x-ray diffraction (XRD). The optical properties were also analyzed by photoluminescence (PL) measurement.

• Proceedings of the Materials Research Society of Korea Conference
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• 한국재료학회 2009년도 춘계학술발표대회
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• pp.16.1-16.1
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• 2009

We have fabricated solution processed oxide semiconductor active layer for thin film transistors (TFTs). The oxide semiconductor layers were prepared by ink-jet printing the sol-gel precursor solution based on doped-ZnO. Inorganic ZnO-based thin films have drawn significant attention as an active channel layer for TFTs applications alternative to conventional Si-based materials and organic semiconducting materials, due to their wide energy band gap, optical transparency, high mobility, and better stability. However, in spite of such excellent device performances, the fabrication methods of ZnO related oxide active layer involve high cost vacuum processes such as sputtering and pulsed laser deposition. Herein we introduced the ink-jet printing technology to prepare the active layers of oxide semiconductor. Stable sol-gel precursor solutions were obtained by controlling the composition of precursor as well as solvents and stabilizers, and their influences on electrical performance of the transistors were demonstrated by measuring electrical parameters such as off-current, on-current, mobility, and threshold voltage. Microstructure and thermal behavior of the doped ZnO films were investigated by SEM, XRD, and TG/DTA. Furthermore, we studied the influence of the ink-jet printing conditions such as substrate temperature and surface treatment on the microstructure of the ink-jet printed active layers and electrical performance. The mobility value of the device with optimized condition was about 0.1-1.0 $cm^2/Vs$ and the on/off current ratio was about $10^6$. Our investigations demonstrate the feasibility of the ink-jet printed oxide TFTs toward successful application to cost-effective and mass-producible displays.

• Transactions on Electrical and Electronic Materials
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• 제5권1호
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• pp.1-6
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• 2004

Zinc sulfide is a semiconductor with wide band gap and high refractive index and hence promising material to be used as ARC on commercial silicon solar cells. Uniform deposition of zinc sulfide (ZnS) by using chemical bath deposition (CBD) method over a large area of silicon surface is an emerging field of research because ZnS film can be used as a low cost antireflection coating (ARC). The main problem of the CBD bath process is the huge amount of precipitation that occurs during heterogeneous reaction leading to hamper the rate of deposition as well as uniformity and chemical stoichiometry of deposited film. Molar concentration of thiorea plays an important role in varying the percentage of reflectance and refractive index of as-deposited CBD ZnS film. Desirable rate of film deposition (19.6 ${\AA}$ / min), film uniformity (Std. dev. < 1.8), high value of refractive index (2.35), low reflectance (0.655) have been achieved with proper optimization of ZnS bath. Decrease in refractive index of CBD ZnS film due to high temperature treatment in air ambiance has been pointed out in this paper. Solar cells of conversion efficiency 13.8 ％ have been successfully achieved with a large area (103 mm ${\times}$ 103 mm) mono-crystalline silicon wafers by using CBD ZnS antireflection coating in this modified approach.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제16권2호
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• pp.1555-1562
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• 2015

Metal oxide semiconductors have been applied in several areas, such as solar cells, sensor, optical elements and displays, due to the high surface area, unique electrical and optical characteristics. Zinc oxide among the metal oxide has excellent physicochemical properties. Zinc oxide is a n-type semiconductor with a wide direct transition band gap of 3.37 eV at room temperature and large exciton binding energy of 60 meV. Cation-doped zinc oxide studies were conducted to complement the electrical and optical characteristics. In this paper, Al-doped ZnO was synthesized by hydrothermal synthesis using microwaves. ZnO was synthesized by adjusting the precursor ratio and using different dopants. The optimal ZnO synthesis conditions for crystal shape and optical properties were determined. The optical properties of aluminum doped zinc oxide were then examined by SEM, XRD, PL, UV-vis absorbance spectrum, and EDS.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.166-166
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• 2007

ZnO는 육방정계(wurtzite) 결정구조를 지니며 상온에서 3.37eV의 wide band gap을 갖는다. ZnO의 엑시톤 결합 에너지는 GaN에 비해 2.5배 높은 60meV로서 고효율의 광소자 적용 가능성이 높다. 또한 고품위의 박막합성이 가능하다. 이러한 특성 때문에 display소자의 투명전극, 광전소자, 바리스터, 압전소자, 가스센서 등에 폭 넓게 응용되고 있다. ZnO박막의 제조는 스퍼터링, CVD, 진공증착법, 열분해법 등이 있다. 본 논문에서는 RF 마그네트론 스퍼터에 의해 제작된 ZnO 박막에 CMP공정을 수행하여 연마율과 비균일도 특성 및 광투과 특성을 연구하였다. ZnO박막은 $2{\times}2Cm$의 Corning glass위에 증착되었다. 로터리 펌프와 유확산 펌프를 이용하여 초기진공을 $2{\times}10^{-6}$ Torr까지 도달시킨 후 Ar과 $O_2$를 주입하였다. 증착은 상온에서 이루어졌으며 공정압력은 $6{\times}10^{-2}$Torr이였다. 초기의 불안정한 상태의 풀라즈마를 안정시키기 위해 셔터를 이용하여 pre-sputtering을 하였다. CMP 공정조건은 플레이튼 속도, 슬러리 유속, 압력은 칵각 60rpm, 90ml/min, $300g/cm^2$으로 일정하게 유지하였으며 헤드속도는 20rpm에서 100rpm까지 증가시키면서 연마특성을 조사하였다. 실리카슬러리의 적합성을 알아보기 위해 DIW와 병행하여 CMP공정을 수행하고 비교 분석하였다. CMP공정 결과 광투과도는 굉탄화된 표면의 확보로 인해 향상된 특성을 보였다. 실리카 슬러리를 사용하여 CMP를 할 경우는 헤드속도는 저속으로 하여야 양호한 연마특성을 얻을 수 있었다.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.115-115
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• 2000

Wide band gap을 갖는 III-V족 반도체인 GaN는 파란색에서 자외선영역에 이르는 발광소자용으로, 그리고 최근에는 전자소자로도 가장 유망한 반도체 중의 하나이다. 하지만 격자상수가 일치하는 적당한 기판이 존재하지 않아 성장된 GaN 박막 내에는 많은 결함들이 존재하게 된다. 일반적으로 가장 널리 쓰이는 기판은 사파이어 기판이 주로 이용되고 있는데 사파이어는 GaN와 격자상수 불일치가 16%에 이르므로 고품질의 GaN 박막을 성장시키기 위해서는 격자상수 불일치를 어느 정도 완화시키면서 초기성장과정의 컨트롤이 매우 중요하다. 이러한 방법들로는 GaN박막 성장 전에 사파이어 기판 질화처리를 하거나 buffer 층을 도입하는 것인데, 이에 관한 많은 연구들이 보고되고 있다. 하지만 각각 두 공정에 관한 연구는 많이 되어 있지만 두 공정사이를 연결해 주는 공정처리법에 관한 연구는 보고되고 있지 않다. 따라서 본 연구에서는 사파이어기판 질화처리를 한 후 buffer 층을 성장시키기 전까지 chamer 내부의 분위기 가스가 GaN 박막성장 거동에 어떤 영향을 주는지에 관해 연구하였다. 질화처리 후 chamber 내부의 분위기 가스가 GaN 박막 성장 거동에 미치는 영향을 연구하기 위하여 두 개의 시편 A,B를 준비하였다. 시편 A는 먼저 사파이어 기판을 유기용매를 이용하여 cleaning 한 후 장비에 장입되었다. 수소분위기하에서 10nsrks 104$0^{\circ}C$에서 가열한 후 30초간 암모니아 유속을 900sccm으로 유지하며 사파이어 기판 질화처리를 수행하였다. GaN buffer 층을 성장하기 위하여 104$0^{\circ}C$에서 56$0^{\circ}C$로 온도를 내리는 과정중 질화처리를 위하여 흘려주었던 암모니아 유속을 차단한 채 수소분위기에서만 온도를 내렸다. 56$0^{\circ}C$에서 GaN buffer 층을 300 성장시킨 후 102$0^{\circ}C$의 고온에서 2$\mu\textrm{m}$ 두께로 GaN 박막을 성장하였다. 시편 B는 질화처리 후 단계부터 GaN 박막성장 단계에 이르기까지 AFM을 이용하여 두 시편의 성장거동을 비교 분석하였다. 두 시편의 표면을 관찰한 결과 시편 A는 2차원적 성장을 하며 매우 매끄러운 표면을 갖는데 반해, 시편 B는 3차원적 성장을 하며 매우 거친 표면을 보였다. 또한 두 시편 A, B를 XRD, PL, Hal 측정으로 분석한 결과 시편 A가 시편 B보다 우수한 구조적, 광학적, 전기적 특성을 보였다.