• Advances in materials Research
• /
• 제2권2호
• /
• pp.77-91
• /
• 2013

High quality nanoparticles of neodymium barium niobium ($NdBa_2NbO_6$) perovskites have been synthesized using an auto ignition combustion technique for the first time. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopy. UV-Visible absorption and photoluminescence spectra of the samples are also recorded. The structural analysis shows that the nano powder is phase pure with the average particle size of 35 nm. The band gap determined for $NdBa_2NbO_6$ is 3.9 eV which corresponds to UV-radiation for optical inter band transition with a wavelength of 370nm. The nanopowder could be sintered to 96% of the theoretical density at $1325^{\circ}C$ for 2h. The ultrafine cuboidal nature of nanopowders with fewer degree of agglomeration improved the sinterability for compactness at relatively lower temperature and time. During the sintering process the wide band gap semiconducting behavior diminishes and the material turns to a high permittivity dielectric. The microstructure of the sintered surface was examined using scanning electron microscopy. The striking value of dielectric constant ${\varepsilon}_r=43$, loss factor tan ${\delta}=1.97{\times}10^{-4}$ and the observed band gap value make it suitable for many dielectric devices.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
• /
• pp.145-145
• /
• 2008

High-k materials have been paid much more attention for their characteristics with high permittivity to reduce the leakage current through the scaled gate oxide. Among the high-k materials, $ZrO_2$ is one of the most attractive ones combing such favorable properties as a high dielectric constant (k= 20 ~ 25), wide band gap (5 ~ 7 eV) as well as a close thermal expansion coefficient with Si that results in good thermal stability of the $ZrO_2$/Si structure. During the etching process, plasma etching has been widely used to define fine-line patterns, selectively remove materials over topography, planarize surfaces, and trip photoresist. About the high-k materials etching, the relation between the etch characteristics of high-k dielectric materials and plasma properties is required to be studied more to match standard processing procedure with low damaged removal process. Among several etching techniques, we chose the inductively coupled plasma (ICP) for high-density plasma, easy control of ion energy and flux, low ownership and simple structure. And the $BCl_3$ was included in the gas due to the effective extraction of oxygen in the form of $BCl_xO_y$ compounds. During the etching process, the wafer surface temperature is an important parameter, until now, there is less study on temperature parameter. In this study, the etch mechanism of $ZrO_2$ thin film was investigated in function of $Cl_2$ addition to $BCl_3$/Ar gas mixture ratio, RF power and DC-bias power based on substrate temperature increased from $10^{\circ}C$ to $80^{\circ}C$. The variations of relative volume densities for the particles were measured with optical emission spectroscopy (OES). The surface imagination was measured by scanning emission spectroscope (SEM). The chemical state of film was investigated using energy dispersive X-ray (EDX).

• Composites Research
• /
• 제35권3호
• /
• pp.201-215
• /
• 2022

본 연구에서는 초고온 환경에서 내화학성 및 열적 안정성이 우수한 지오폴리머 기반의 알루미노실리케이트 레진과 세라믹 섬유를 활용한, 목표주파수 X-band(8.2 GHz to 12.4 GHz)에서 전자파를 흡수하는 세라믹 복합재(Radar-absorbing ceramic composite, RACC)를 구현하였다. 주 성분이 FeSi인 판형 구조의 샌더스트 자성 입자를 분산시킨 알루미노실리케이트 레진은 목표 주파수 대역에서 자성 및 유전손실 특성을 발휘하였고, 입도와 무게분율별 유전특성을 Cole-Cole Plot으로 표현하였다. 샌더스트가 분산된 알루미노실리케이트 레진의 미세구조, 화학적 성분 및 결정, 자기 및 열적 특성 등을 분석하기 위해 SEM, EDS, VSM 및 TGA를 측정하였다. 샌더스트의 입도 크기 35 ㎛, 무게분율 40 wt.%를 분산시킨 레진의 유전손실 특성을 활용하여, X-band에서 약 1.51 GHz 대역폭에 대해 -10 dB 이하의 반사손실 성능을 발휘하는 단층형(t = 1.585 mm) RACC를 설계 및 제작하였다. 제작된 RACC의 초고온(25℃ to 1,000℃)에서 전자파 흡수 거동을 살피기 위해 개발된 초고온 환경 자유공간측정 장비를 활용하여 X-band 대역에서 그 성능을 검증하였다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
• /
• pp.169-169
• /
• 2008

To keep pace with scaling trends of CMOS technologies, high-k metal oxides are to be introduced. Due to their high permittivity, high-k materials can achieve the required capacitance with stacks of higher physical thickness to reduce the leakage current through the scaled gate oxide, which make it become much more promising materials to instead of $SiO_2$. As further studying on high-k, an understanding of the relation between the etch characteristics of high-k dielectric materials and plasma properties is required for the low damaged removal process to match standard processing procedure. There are some reports on the dry etching of different high-k materials in ICP and ECR plasma with various plasma parameters, such as different gas combinations ($Cl_2$, $Cl_2/BCl_3$, $Cl_2$/Ar, $SF_6$/Ar, and $CH_4/H_2$/Ar etc). Understanding of the complex behavior of particles at surfaces requires detailed knowledge of both macroscopic and microscopic processes that take place; also certain processes depend critically on temperature and gas pressure. The choice of $BCl_3$ as the chemically active gas results from the fact that it is widely used for the etching o the materials covered by the native oxides due to the effective extraction of oxygen in the form of $BCl_xO_y$ compounds. In this study, the surface reactions and the etch rate of $Al_2O_3$ films in $BCl_3/Cl_2$/Ar plasma were investigated in an inductively coupled plasma(ICP) reactor in terms of the gas mixing ratio, RF power, DC bias and chamber pressure. The variations of relative volume densities for the particles were measured with optical emission spectroscopy (OES). The surface imagination was measured by AFM and SEM. The chemical states of film was investigated using X-ray photoelectron spectroscopy (XPS), which confirmed the existence of nonvolatile etch byproducts.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
• /
• pp.235.1-235.1
• /
• 2015

Artificially-engineered materials, whose electromagnetic properties are not available in nature, such as negative reflective index, are called metamaterials (MMs). Although many scientists have investigated MMs for negative-reflective-index properties at the beginning, their interests have been extended to many other fields comprising perfect lenses. Among various kinds of MMs, metamaterial absorbers (MM-As) mimic the blackbody through minimizing transmission and reflection. In order to maximize absorption, the real and the imaginary parts of the permittivity and permeability of MM-As should be adjusted to possess the same impedance as that of free space. We propose a dual-wide-band and polarization-independent MM-A. It is basically a triple-layer structure made of metal/dielectric multilayered truncated cones. The multilayered truncated cones are periodically arranged and play a role of meta-atoms. We realize not only a wide-band absorption, which utilizes the fundamental magnetic resonances, but also another wide-band absorption in the high-frequency range based on the third-harmonic resonances, in both simulation and experiment. In simulation, the absorption bands with absorption higher than 90% are 3.93 - 6.05 GHz and 11.64 - 14.55 GHz, while the experimental absorption bands are in 3.88 - 6.08 GHz and 9.95 - 13.84 GHz. The physical origins of these absorption bands are elucidated. Additionally, it is also polarization-independent because of its circularly symmetric structures. Our design is scalable to smaller size for the infrared and the visible ranges.

• 한국전자파학회논문지
• /
• 제18권7호
• /
• pp.796-808
• /
• 2007

이 논문에서는 split-ring 공진기와 spiral 공진기를 complementary 형태로 구현한 새로운 형태의 두 가지 마이크로스트립 대역저지 필터를 제안하였다. 첫 번째는 마이크로스트립 전송 선로의 중앙 선로에 세 개의 split-ring 공진기를 일렬로 배열시켜 에칭 시킨 것이다. 중앙 선로에 구현된 세 개의 split-ring 공진기와 수직으로 시간에 따라 변하는 전계가 걸리면 특정 공진 주파수에서 유효 투자율이 음이 되는 현상이 벌어지며, 이에 따라 전파가 더 이상 진행하지 못하게 된다. 이는 특정 공진 주파수에서 대역저지 현상이 나타나는 것을 의미한다. 두 번째는 첫 번째 것과 비슷하게 마이크로스트립의 중앙 선로에 spiral 공진기를 세 개 나열하여 에칭하였다. Spiral 공진기는 그 축에 수직한 방향으로 전계가 걸렸을 때 특정 공진 주파수에서 self-resonance 현상이 일어나며, 이것이 대역저지 특성으로 나타난다. 제안된 두 필터는 쉽게 공진 주파수와 대역저지 폭을 결정할 수 있고, 매우 작은 크기를 갖으며, 통과대역 내에서 삽입손실이 거의 없으며, 매우 날카로운 스커트 특성을 갖는다. 또한 제작하기 쉽고, 향후 MMIC에 적용하기 쉬울 것으로 예상한다.

• 한국전자통신학회논문지
• /
• 제10권10호
• /
• pp.1189-1196
• /
• 2015

본 논문에서는 GPS/WiMAX/WLAN 시스템에 적용 가능한 다중밴드 대역을 갖는 모노폴 안테나를 설계, 제작 및 측정 하였다. 제안된 안테나는 마이크로스트립 급전을 바탕으로 두 개의 사각 링과 한 쌍의 L 선로로 구성되어 삼중 대역의 특성을 갖도록 설계하였다. 최적화된 수치를 얻기 위해 상용 툴인 HFSS을 사용하여 시뮬레이션을 수행하였다. 제안된 안테나는 $27.0{\times}54.0{\times}1.0mm3$의 크기로 유전율 4.4인 RF 4 기판 위에 제작되었다. 제작 결과, 제안된 안테나는 -10dB 임피던스 대역폭을 기준으로 300 MHz(1.325~1.625 GHz), 400 MHz (2.275~2.675 GHz), 그리고 600 MHz (3.15~3.75 GHz)의 대역폭을 얻었다. 또한 제안된 안테나는 요구되는 3개 대역에서 측정된 이득과 방사패턴의 특성을 얻었다.

• 한국전자통신학회논문지
• /
• 제11권9호
• /
• pp.841-848
• /
• 2016

본 논문에서는 DGS(: Defected Ground Structure)을 적용하여 WLAN 시스템에 적용 가능한 모노폴 안테나를 설계, 제작 및 측정하였다. 제안된 안테나는 마이크로스트립 급전을 바탕으로 두 개의 선로와 DGS를 갖도록 설계하여 이중대역 특성을 갖도록 하였다. 상용 툴인 HFSS을 사용하여 $W_2$, $L_{10}$, $W_3$과 DGS 파라미터에 대한 시뮬레이션을 수행하여 최적화된 수치를 얻었다. 제안된 안테나는 $21.0{\times}36.0{\times}1.6mm^3$의 크기로 유전율 4.4인 FR-4 기판 위에 설계 및 제작되었다. 제작 결과, 제안된 안테나는 -10 dB 임피던스 대역폭을 기준으로 700 MHz (2.10~2.80 GHz) 그리고 1,780 MHz(5.02~6.80 GHz)의 대역폭을 얻었다. 또한, 제안된 안테나의 측정 이득과 방사패턴 특성이 요구되는 이중대역에서 제시되었다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1992년도 하계학술대회 논문집 B
• /
• pp.744-746
• /
• 1992

In this study, we investigated structural, electrical characteristics and studied the conditions which improved hydrostatic constants in hydrophones as we changed x = 0.1, 0.25, 0.35, 0.4 and y = 0.04, 0.08, 0.12, 0.16 in $(Pb_{1-x}Ca_x)[(Mg_{1/3}Nb_{2/3})_yTi_{1-0.01}Mn_{0.01}]O_3$ ceramics in which Ca was substituted with Pb and $Pb(Mg_{1/3}Nb_{2/3})O_3$ was added to decrease sintering temperature in $PbTiO_3$. When Ca was substituted 0.25[mol], the largest electro-mechanical anisotropy ($k_t/k_p$) was found ($k_t{\fallingdotseq}50,k_p{\fallingdotseq}4$), and the less $Pb(Mg_{1/3}Nb_{2/3})O_3$ and the stronger poling field, the larger this anisotropy was. When Ca=0.25[mol], $Pb(Mg_{1/3}Nb_{2/3})O_3=0.08[mol]$ were substituted, ($k_t/k_p$)(=12, 3) was large, permittivity was low and hydrostatic constants were high. Therefore, this composition is promising as wide band ultrasonic devices in water.

• Journal of Electrical Engineering and Technology
• /
• 제10권4호
• /
• pp.1700-1711
• /
• 2015

In the last decade it has been witnessed significant developments in the area of nano particles and nano scale fillers on electrical, thermal, and mechanical properties of polymeric materials such as resins, varnishes, enamel and bakelites. The electric and thermal properties were more important in the electrical equipments for both steady state and transient state conditions. This paper deals with the characterization of the electric and thermal properties of the pure varnish and zirconia (ZrO₂) filler mixed varnish. The electric properties such as dielectric loss (tan δ), dielectric constant (ε), dielectric strength and partial discharge voltage were analyzed and detailed for different samples. It was observed that zirconia nano filler mixed varnish has the superior dielectric and thermal properties when compared to those of standard varnish. It has shown that at power frequency the 1wt% nano composite sample has the higher permittivity value when compared to other samples. It has been examined that the 1wt% sample was having higher inception and extinction voltages when compared to other samples. It has been observed that 1wt% sample has higher dielectric strength when compared with other samples. There has been an improvement of thermal property by adding few weight percent of zirconia nano fillers. There was not much variation in glass transition among the nano mixed composites. The weight loss was improved at 1wt% of the zirconia nano fillers.