• 한국세라믹학회지
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• 제37권7호
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• pp.632-637
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• 2000

Thermoelectric conversion properties of commercial Fe-Si2 and Fe-Si alloy ingots prepared by RF inductive furnace were investigated. As sintering temperature increased, density of the specimen increased and the phase transformation from metallic phases ($\varepsilon$-FeSi, ${\alpha}$-Fe2Si5) to semiconducting phase (${\beta}$-FeSi2) occurred more effectively. The FeSi phase was detected even after 100hrs of annealing treatment. For the Fesi1.95∼FeSi2.05 specimens prepared by RF inductive furnace, the thermoelectric property improved as the composition of the specimen approached to stoichiometric composition FeSi2. Electrical conductivity of the specimen increased with increasing temperatures showing typical semiconducting behavior. From the electrical conductivity measurements, activation energy in the intrinsic region (above about 700 K) was calculated to be approximately 0.46 eV. In spite of non-doping, the Seebeck coefficient for every specimen exhibited p-type conduction due to Si deficiency. Its maximum value was located at about 475 K, and then decreased abruptly with increasing temperatures. The power factor was governed by the Seebeck coefficient of the specimen more significantly than by electrical conductivity.

• 한국전기전자재료학회논문지
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• 제27권8호
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• pp.510-515
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• 2014

Thin films of cubic $Na_{0.6}WO_3$, which is one of the sodium tungsten bronze, were fabricated by rf sputtering for the electrode applications in integrated sensors and actuators. A single-phase cubic $Na_{0.6}WO_3$ sputtering target of power type was prepared by conventional solid-state reaction. Thin films were deposited from the powder target, and the as-deposited films were amorphous, thus they annealed by tube furnace or RTP for crystallization. Thin films having cubic phase $Na_xWO_3$ were fabricated by the optimization of sputtering and post-annealing conditions, but single-phase cubic $Na_{0.6}WO_3$ thin films were not obtained. Although the films were not in single phase, they had good electrical conduction properties showing electrical resistivities of $10-4{\Omega}{\cdot}cm$ order.

• 한국전기전자재료학회논문지
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• 제24권6호
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• pp.468-472
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• 2011

Conductive $SrMoO_3$ thin films were fabricated by RF magnetron sputtering with the powder-type sputtering target, and annealed for crystallization. When RTP (rapid thermal processing) in vacuum was applied, the fabricated thin films showed the mixed phases of $SrMoO_3$ and $SrMoO_4$, but $SrMoO_3$ phase could be promoted by the lowering of the working pressure during deposition. In order to eliminate $O_2$ gas during deposition and annealing, further lowering of the working pressure and furnace annealing in hydrogen atmosphere were tried. With the optimization of the deposition and annealing conditions, the thin film with nearly single-phase of $SrMoO_3$ was obtained, and it showed good electrical conduction properties with a low resistivity of $2.5{\times}10^{-3}{\Omega}{\cdot}cm$ at room temperature.

• 전자통신동향분석
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• 제33권6호
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• pp.12-23
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• 2018

In this paper, we review the technical trends of diamond and gallium oxide ($Ga_2O_3$) semiconductor technologies among ultra-wide bandgap semiconductor technologies for harsh environments. Diamond exhibits some of the most extreme physical properties such as a wide bandgap, high breakdown field, high electron mobility, and high thermal conductivity, yet its practical use in harsh environments has been limited owing to its scarcity, expense, and small-sized substrate. In addition, the difficulty of n-type doping through ion implantation into diamond is an obstacle to the normally-off operation of transistors. $Ga_2O_3$ also has material properties such as a wide bandgap, high breakdown field, and high working temperature superior to that of silicon, gallium arsenide, gallium nitride, silicon carbide, and so on. In addition, $Ga_2O_3$ bulk crystal growth has developed dramatically. Although the bulk growth is still relatively immature, a 2-inch substrate can already be purchased, whereas 4- and 6-inch substrates are currently under development. Owing to the rapid development of $Ga_2O_3$ bulk and epitaxy growth, device results have quickly followed. We look briefly into diamond and $Ga_2O_3$ semiconductor devices and epitaxy results that can be applied to harsh environments.

• 한국재료학회지
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• 제20권9호
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• pp.494-499
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• 2010

Tin oxide thin films were prepared on borosilicate glass by rf reactive sputtering at different deposition powers, process pressures and substrate temperatures. The ratio of oxygen/argon gas flow was fixed as 10 sccm / 60 sccm in this study. The structural, electrical and optical properties were examined by the design of experiment to evaluate the optimized processing conditions. The Taguchi method was used in this study. The films were characterized by X-ray diffraction, UV-Vis spectrometer, Hall effect measurements and atomic force microscope. Tin oxide thin films exhibited three types of crystal structures, namely, amorphous, SnO and $SnO_2$. In the case of amorphous thin films the optical band gap was widely spread from 2.30 to 3.36 eV and showed n-type conductivity. While the SnO thin films had an optical band gap of 2.24-2.49 eV and revealed p-type conductivity, the $SnO_2$ thin films showed an optical band gap of 3.33-3.63 eV and n-type conductivity. Among the three process parameters, the plasma power had the most impact on changing the structural, electrical and optical properties of the tin oxide thin films. It was also found that the grain size of the tin oxide thin films was dependent on the substrate temperature. However, the substrate temperature has very little effect on electrical and optical properties.

• 한국전기전자재료학회논문지
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• 제18권11호
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• pp.1043-1047
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• 2005

To investigate the electrical properties of the ZnO films which are interested in the next generation of short wavelength LEDs and Lasers, our ZnO thin films were deposited by RF sputtering system. At sputtering process of ZnO thin films, substrate temperature, work pressure respectively is $300^{\circ}C$ and 5.2 mTorr, and the purity of target is ZnO 5N. The thickness of ZnO thin films was about $2.1\;{\mu}m$ at SEM analysis after sputtering process. Phosphorus (P) and arsenic (As) were diffused into the undoped ZnO thin films sputtered by RF magnetron sputtering system in ampoule tube which was below $5\times10^{-7}$ Torr. The dopant sources of phosphorus and arsenic were $Zn_3P_2$ and $ZnAs_2$. Those diffusion was perform at 500, 600, and $700^{\circ}C$ during 3 hr. We found the diffusion condition of the conductive ZnO films which had n- and p-type properties. Our ZnO thin film has not only very high carrier concentration of above $10^{17}/cm^3$ but also low resistivity of below $2.0\times10^{-2}\;{\Omega}cm$.

• 한국전자파학회논문지
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• 제16권2호
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• pp.134-138
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• 2005

본 논문에서는 능동 역지향성 배열 안테나용의 마이크로파 공액 위상변위기에 관한 새로운 구조를 제안하였다. 본 논문에서 제안된 공액 위상변위기는 Single-Balanced 혼합기를 응용한 것으로, 일반적인 혼합기와 달리, LO 및 RF 신호의 결합과 임피던스 매칭의 복잡성을 줄이기 위해서 2-포트 구조를 채택하였으며, 병렬 연결된 두 개의 Single-Ended 혼합기에 180도 위상반전 회로를 삽입하여, 공액 위상변위기 설계에서 가장 큰 문제가 되는 IF 출력단의 RF 누설성분을 억제하였다. 동작 주파수는 LO 4 GHz, RF 2.01 GHz, IF 1.99 GHz이다. 제작된 공액 위상변위기는 9 dBm의 LO전력에서 변환손실은 -7 dB, 1-dB 억압점 15 dBm의 특성을 보인다. 공액 위상 변위기의 가장 중요한 파라미터인 RF/IF 격리도는 25 dB에 달한다.

• Korean Chemical Engineering Research
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• 제46권1호
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• pp.50-55
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• 2008

RF plasma CVD법을 이용하여 금속 촉매(Fe)가 증착된 $SiO_2$ 기판 위에 $H_2$와 $C_2H_2$의 혼합가스를 사용하여 증착된 탄소나노튜브(carbon nanotube, CNT)의 특성에 대한 기판의 온도의 영향을 조사하였다. $SiO_2$ 위에 철 촉매는 RF 마그네트론 스퍼터에 의해 만들어졌다. 고 순도의 나노튜브 박막을 얻기 위해서 기판 홀더 위에 접지된 그리드 메쉬 커버를 설치하였다. 증착된 CNT의 표면 미세구조 및 화학적 구조를 SEM, Raman, XPS, 그리고 TEM으로 측정하였다. 증착된 CNT 박막들은 대나무 같은 다중벽 구조를 가지는 탄소 파이버 형태였으며 $55^{\circ}C$에서 보다 $600^{\circ}C$에서 보다 더 치밀한 구조를 보이나 $650^{\circ}C$에서는 밀도가 다소 감소함을 알 수 있었다.

• 한국정보통신학회논문지
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• 제16권5호
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• pp.1023-1028
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• 2012

본 논문에서는 비접촉 마이크로웨이브 프루브 시스템의 I/Q demodulator를 위한 MMIC (Monolithic Microwave Integrated Circuit) mixer chip을 GaAs p-HEMT 공정의 Schottky 다이오드를 이용하여 설계 및 제작하였다. 프루브 시스템의 I/Q demodulator 구조를 단순화하기 위해 single balanced 구조의 mixer를 채택하였다. Single balanced mixer에서 $90^{\circ}$hybrid coupler와 ${\lambda}/4$ 전송선로를 이용하여 $180^{\circ}$hybrid를 설계하였으며 이를 MIM 커패시터와 spiral 인덕터를 이용하여 구현함으로써 mixer chip의 크기를 줄일 수 있었다. On-wafer 측정 결과, 본 논문의 MMIC mixer는 1650MHz ~ 2050MHz의 RF 및 LO 주파수 대역을 포함하고 있으며, 응용 주파수 대역 내에서 RF 및 LO의 변화에 대해 약 12dB 이하의 평탄한 변환손실(conversion loss) 특성을 나타내었다. 또한, MMIC mixer chip은 $2.5mm{\times}1.7mm$의 초소형 크기를 가지며 LO-IF 및 RF-IF의 격리도는 각각 43dB 및 23dB 이상의 특성을 나타내었다.

• 한국항행학회논문지
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• 제24권6호
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• pp.593-600
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• 2020

해양 IoT 서비스를 위한 장치들은 해양 환경에 강인해야 한다. 특히 바닷물 속에 부유하는 전송 장치는 바닷물의 영향을 덜 받도록 설계되어야 한다. 본 연구에서는 전자 어구 실명제 모니터링 시스템에서 어구 상태를 감시하는 부이에 내장되는 안테나를 설계하고 제작한 결과를 보이고 있다. 안테나의 주파수 대역은 920 MHz이고, 부이의 초소형과 경량화를 위해 PCB 패턴 안테나 구조로 설계 제작되었다. 시뮬레이션 결과 제안한 안테나를 내장한 부이가 바닷물 속에 잠기는 정도가 심할수록 반사 계수 증 RF 특성이 저하되지만 빔의 방사 각도는 안테나 하층부에서 점점 상층부로 옮겨가는 것을 확인하였다. 즉 바닷물의 영향을 많이 받을수록 전파 성능은 저하되지만 방사 특성은 해양 IoT 서비스 환경에 적합하다는 것을 확인하였다. 향후 RF 성능을 개선할 수 있는 안테나 구조를 변경 설계하면 제안한 안테나와 부이는 LPWA (low power wide area) 기반 IoT 네트워크 구현에 기여할 것으로 기대된다.