• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.179-179
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• 2008

$BaTiO_3$를 기본조성으로 하는 PTC 써미스터는 Curie 온도이상에서 저항이 급격히 상승하는 산화물 반도체 세라믹이다. 이러한 성질을 이용하여 degaussing 소자, 정온 발열체, 온도센서, 전류 제한소자 등 상업적으로 여러 분야에서 연구되고 있다. 또한 원가절감 등을 위하여 Ni 내부전극을 사용하여 환원 분위기에서 소결하는 칩 타입에 대한 연구가 진행되고 있다. 본 연구에서는 Sm 함량(0.1at%~1.0at%)을 달리한 $BaTiO_3$(Si, Mn, Ca) 계를 선택하여 3%$H_2/N_2$ 분위기에서 1200~$1260^{\circ}C$, 2h 소결한 후 공기 중에서 재산화 처리하고 재산화 시간에 따른 PTC 특성 변화에 대하여 고찰하였다. 재산화 온도와 시간은 각각 $800^{\circ}C$와 0.5h~10h으로 하였다. Sm 함량을 달리하여 환원 분위기에서 소결한 시편의 미세구조와 PTC 특성과의 상관관계를 관찰한 결과, 소결온도가 낮을수록 PTC 특성은 좋아졌으며, 상온 비저항은 Sm 함량이 높아질수록 낮아졌다. 또한 Sm 함량이 높아질수록 jumping ratio$(R_{max}/R_{25^{\circ}C})$는 낮아졌다. 재산화 시간에 따른 PTC 특성은 다소 떨어졌지만 소결온도에 따라 달리 나타났다. Jumping ratio$(R_{max}/R_{25^{\circ}C})$는 Sm을 0.7 at% 첨가한 계에서 재산화를 1시간 처리한 시편에서 가장 우수하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.685-688
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• 2003

[ $(Ba,Sr,Ca)TiO_3$ ] powders, prepared by the sol-gel method, were mixed with an organic vehicle and the BSCT thick films were fabricated by the screen printing techniques on alumina substrates. The grain size decreased with increasing amounts of $MnO_2$, and the BSCT(50/40/10) thick film doped with 1wt% $MnO_2$ showed a value of 6.5mm. The thickness of thick films by four-cycle on printing/drying was approximately 100mm. The relative dielectric constant, dielectric loss and tunability of the BSCT(S0/40/10) thick films doped with 1.0wt% $MnO_2$ were 1296, 0.61% and 11.18%, respectively.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1012-1220
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• 1994

BaTiO3 ceramics doped with 0.1 to 4.0 mol% Nb2O5 were prepared by conventional solid stage sintering process, so as to investigate the effect of the amount of Nb2O5 on the dielectric properties and complex impedance patterns of barium titanates. From the measurement of capacitance, we found that the dielectric constant of BaTiO3 samples with 1 mol% or more Nb2O5 remained approximately constant around room temperature with values higher than 2500. In this paper, the effect of impurity content as well as temperature on complex impedance patterns was discussed in detail. In particular, the grain and grain boundary behavior of samples which showed PTCR characteristics was discussed in terms of measuring temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.304-304
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• 2010

최근 생활에 편리하며 휴대하기 좋은 전자기기들이 개발되고 있다. 휴대폰이나 MP3와 같은 전자기기들은 거의 필수품이라고 할 정도로 우리의 일상생활에 근접하여 있다. 그 종 대표적으로 휴대폰의 종류로 스마트폰과 같은 터치스크린을 이용한 사례는 점차 상승하고 있으며 시간이 지날수록 그 수요는 더욱 많아지고 있다. 때문에 몰입감 제공을 위하여 햅틱장치의 채용이 일반화 되고 있다. 햅틱장치란 가상환경이나 원거리에 있는 환경과 사용자가 상호 작용할 때 사용자에게 촉감이나 힘의 정보를 전달하여 주는 장치로 진동 및 회동 저항에 의해 사용자로 하여금 촉감들 느낄 수 있도록 하는 장치를 뜻한다. 즉, 현실감을 전달을 중점으로 하는 햅틱장치는 빠른 응답 속도와, 진동의 주파수와 크기는 독립적으로 제어가 가능해야 하며 기계적 수용기들을 직접적으로 자극할 수 있어야 한다. 하지만 모바일 햅틱장치의 경우 크기 및 소비전력의 문제로 모든 스펙을 만족하기에는 어려워 좀 더 한정적인 느낌을 제공할 수 없다. 현재까지 모바일 장치에서 햅틱 피드백을 위하여 진동모터나, 솔레노이드, 압전 액츄에이터 등이 많이 사용되어 지고 있다. 그 중 압전 액츄에이터는 입력에너지를 기계적 출력에너지로 변환되는 효과를 이용 한 것으로 압력 센서, 초음파 센서 등 많은 분야에서 응용되고 있으며 변위 범위는 작지만, 크기가 매우 작고 변위 정밀도가 높으며 발생력과 응답속도가 빠르다는 장점이 존재한다. 이를 이용한 햅틱 압전 엑츄에이터의 제작에 사용되는 압전 세라믹스는 높은 전기적 특성을 가질수록 더 졸은 효율을 가지며 이로 인하여 보다 좋은 전기적 특성을 가지는 압전 세라믹스를 필요로 한다. 현재 많이 사용되는 PZT계 세라믹스는 우수한 전기적 특성으로 많이 사용되고 있지만 Pb의 유독성으로 인한 환경문제로 Pb가 포함된 제품을 제한하고 있어 현재 Lead-free의 연구가 이루어지고 있다. Lead-free중 Ba$(Ti_{0.8}Zr_{0.2})O_3$(BZT)는 PZT계 세라믹스를 대체할 차세대 압전 재료로 주목받고 있다. 일반적으로 Lead-free의 압전계수($d_{33}$=100~300pC/N)는 비교적 낮은 값을 보이지만 BZT의 압전계수(BZT $d_{33}$~620pC/N)는 PZT계 세라믹스의 압전계수($d_{33}$=500~600pC/N)와 비교하여 부족하지 않은 압전계수를 보여주며 PZT를 대체할 재료로 주목받고 있다. 본 실험은 햅틱 압전 엑츄에이터용 무연 압전세라믹스의 제작을 위하여 Ba$(Ti_{0.8}Zr_{0.2})O_3-(Ba_{0.7}Ca_{0.3})-TiO_3$(BZT -BCT)의 조성으로 유전 및 압전 특성을 조사하였다.

• Korean Journal of Materials Research
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• v.4 no.4
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• pp.453-458
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• 1994

$(Ba_{0.5}Sr_{0.5)/TiO_3$(BST) thin films were prepared for the application of 256 Mb DRAM by RF magnetron sputtering. The crystallinity of BST thin films increased with increasing deposition tempera lure. The composition of thin films was $(Ba_{0.48}Sr_{0.48)/TiO_{2.93}$ Pt/Ti barrier layer suppressed the diffusion of Si into BST layer. The films showed a dielectric constant of 320 and a dissipation factor of 0.022 at 100 kHz. the change of capacitance of the films with applied voltage was small, showing paraelectric property. The charge storage density and leakage current density were 40fC/$\mu \textrm{m}^{2}$ and 0.8$\mu A/\textrm{cm}^2$, respectively at a field of 0.15 MV/cm. The BST films obtained by RF magnetron sputtering appeared to be potential thin film capacitors for 256 Mb DRAM application.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.2
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• pp.339-341
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• 2012

The high Tc superconductor of YBCO system with the nominal composition of precursor was prepared from mixed powders of $Y_2O_3$, $BaCO_3$, CuO and $TiO_2$ by the thermal pyrolysis method. The effect of $TiO_2$ doping to Y based ceramics superconductors fabricated by the thermal pyrolysis reaction, to investigate the effect of the dopant on the superconductivity. The voltage appearing across the field-cooled HTS sample increased with external magnetic field. The improvement of critical current property as well as the mechanical property is important for the application. The improvement of the critical current can be achieved by forming the nano size defect working as a flux pining center inside the superconductor. We simply added $TiO_2$ to starting materials to dope $TiO_2$ and observed an increase in the trapped field and the critical current density up to at least 5 wt % $TiO_2$. The $TiO_2$ was converted to fine $BaTiO_3$ particles which were trapped in YBCO matrix during the sintering process. We observed a peak effect of Jc that can be attributed to $TiO_2$ doping and results suggest that introducing a proper amount of pinning centers can significantly enhance current density.

• Journal of Powder Materials
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• v.16 no.1
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• pp.33-36
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• 2009

In order to increase the magnetic loss for electromagnetic(EM) wave absorption, the soft magnetic $Fe_{73}Si_{16}B_7Nb_3Cu_1$(at%) alloy strip was used as the basic material in this study. The melt-spun strip was pulverized using an attrition mill, and the pulverized flake-shaped powder was crystallized at $540^{\circ}C$ for 1h to obtain the optimum grain size. The Fe-based powder was mixed with 2 wt% $BaTiO_3$, $0.3{\sim}0.6$ wt% carbon black, and polymer-based binders for the improvement of electromagnetic wave absorption properties. The mixture powders were tape-cast and dried to form the absorption sheets. After drying at $100^{\circ}C$ for 1h, the sheets of 0.5 mm in thickness were made by rolling at $60^{\circ}C$, and cut into toroidal shape to measure the absorption properties of samples. The characteristics including permittivity, permeability and power loss were measured using a Network Analyzer(N5230A). Consequently, the properties of electromagnetic wave absorber were improved with the addition of both $BaTiO_3$ and carbon black powder, which was caused by the increased dielectric loss of the additive powders.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1587-1588
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• 2006

Tn this paper, PCB (Printed Circuit Board) embedded $BaTiO_3$ MIM capacitors were designed, fabricated, and characterized for low cost organic SOP applications by using 3-D EM simulator and low temperature processes. Size of electrodes and thickness of high dielectric films are optimized for improving the performance characteristics of the proposed embedded MIM capacitors at high frequency regime. The selected thicknesses of the $BaTiO_3$ film are $12{\mu}m$, $16{\mu}m$, and $20{\mu}m$. The fabricated MIM capacitor with dielectric constant of 30 and thickness of $12{\mu}m$ has capacitance density of $21.5p\;F/mm^2$ at 100MHz, maximum quality factor of 37.4 at 300 MHz, a quality factor of 30.9 at 1GHz, self resonant frequency of 5.4 GHz, respectively. The measured capacitances and quality factors are well matched with 3-D EM simulated ones. These embedded capacitors are promising for SOP based advanced electronic systems with various functionality, low cost, small size and volume.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.4
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• pp.212-215
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• 2018

The phase evolution, microstructure, and microwave dielectric properties of $Ba(Mg_{0.5-2x}Y_{2x}W_{0.5-x}Ti_x)O_3$ (x = 0.005~0.05) ceramics sintered at $1,700^{\circ}C$ for 1h were investigated. All compositions exhibited a 1:1 ordered cubic perovskite structure. The field emission scanning electron microscopy image revealed a dense microstructure in all the compositions. As the value of x increased, the lattice parameter, dielectric constant, and quality factor increased. The temperature coefficient of resonant frequency changed from $-19.6ppm/^{\circ}C$ to $-5.9ppm/^{\circ}C$ with increasing x value. The dielectric constant, quality factor, and temperature coefficient of resonant frequency of $Ba(Mg_{0.40}Y_{0.10}W_{0.45}Ti_{0.05})O_3$ were 21.7, 132,685 GHz, and $-5.9ppm/^{\circ}C$, respectively.

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.05a
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• pp.114-114
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• 2002