• 한국세라믹학회지
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• 제43권7호
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• pp.421-426
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• 2006

[ $(BaSr)TiO_3$ ] thick films were prepared by tape casting method, using $BaTiO_3\;and\;SrTiO_3$ powder slurry in order to investigate dielectric properties i.e. dielectric constant, ${\varepsilon}_r$, Curie temperature, $T_c$. Grain growth within $(BaSr)TiO_3$ thick films was observed with increasing weight ratio of $BaTiO_3$. This observation can be explained by phenomena of substitution of $Sr^{2+}$ ion for $Bi^{2+}$ ion in the $BaTiO_3$ system. Also, the Curie temperature in $(BaSr)TiO_3$ thick films was shifted to lower temperature range with increasing $ SrTiO_3$. Furthermore, Curie temperature having maximum dielectric constant was in the range of $-40^{\circ}C\;to\;30^{\circ}C$, and hence sharper phase transformation occurred at Curie temperature. There occurred decrease in tunability and k-factor of $(Ba_{0.6}Sr_{0.4})TiO_3$ calculated from the dielectric constant, ${\varepsilon}_r$ above Curie temperature. In addition, above the $60^{\circ}C$, phase fixation was observed. This means that internal stress relief occurred with increasing $90^{\circ}$ domains.

• 한국세라믹학회지
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• 제50권2호
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• pp.157-162
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• 2013

The need for lead-free piezoceramics has caused a renewal of interest in $BaTiO_3$-based systems. Recently, it was found that ceramics in the $(Ba,Ca)(Zr,Ti)O_3$ system have properties comparable to those of $Pb(Zr,Ti)O_3$. However, these ceramics require rather high sintering temperatures of $1450-1550^{\circ}C$. In this work, the effect of $TiO_2$ and CuO addition on the sintering behavior, microstructure, dielectric and piezoelectric properties of $(Ba_{0.85}Ca_{0.15})(Zr_{0.1}Ti_{0.9})O_3$ (BCTZ) ceramics will be discussed. BCTZ ceramics were prepared by the mixed oxide route and 1 mol % of $TiO_2$ or CuO was added. Undoped and doped ceramics were sintered at $1350^{\circ}C$ for 1-5 h. CuO was found to be a very effective sintering aid, with samples sintered for 1 h at $1350^{\circ}C$ having a bulk density of 95% theoretical density; however the piezoelectric properties were greatly reduced, probably due to the small grain size.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.319-319
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• 2013

Even though the fabrication methods of metal oxide based thin film capacitor have been well established such as RF sputtering, Sol-gel, metal organic chemical vapor deposition (MOCVD), ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD), an applicable capacitor of printed circuit board (PCB) has not realized yet by these methods. Barium Strontium Titanate (BST) and other high-k ceramic oxides are important materials used in integrated passive devices, multi-chip modules (MCM), high-density interconnect, and chip-scale packaging. Thin film multi-layer technology is strongly demanded for having high capacitance (120 nF/$mm^2$). In this study, we suggest novel multi-layer thin film capacitor design and fabrication technology utilized by plasma assisted deposition and photolithography processes. Ba0.6Sr0.4TiO3 (BST) was used for the dielectric material since it has high dielectric constant and low dielectric loss. 5-layered BST and Pt thin films with multi-layer sandwich structures were formed on Pt/Ti/$SiO_2$/Si substrate by RF-magnetron sputtering and DC-sputtering. Pt electrodes and BST layers were patterned to reveal internal electrodes by photolithography. SiO2 passivation layer was deposited by plasma-enhanced chemical vapor deposition (PE-CVD). The passivation layer plays an important role to prevent short connection between the electrodes. It was patterned to create holes for the connection between internal electrodes and external electrodes by reactive-ion etching (RIE). External contact pads were formed by Pt electrodes. The microstructure and dielectric characteristics of the capacitors were investigated by scanning electron microscopy (SEM) and impedance analyzer, respectively. In conclusion, the 0402 sized thin film multi-layer capacitors have been demonstrated, which have capacitance of 10 nF. They are expected to be used for decoupling purpose and have been fabricated with high yield.

• 마이크로전자및패키징학회지
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• 제11권1호
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• pp.87-96
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• 2004

폴리머/세라믹 복합체는 유기기판용 내장형 커패시터의 가장 유망한 재료다. 폴리머/세라믹 복합체의 유효유전상수를 예측하는 것은 복합재료의 설계에 있어 매우 중요하다. 본 논문에서는 크기가 다른 5가지 $BaTiO_3$ 분말을 이용하여 분말함량에 따른 에폭시/$BaTiO_3$ 복합 내장형 커패시터 필름의 유전상수를 측정하였다. 그 측정 결과를 여러 가지 이론식들에 최소 자승법을 이용해 fitting하여 폴리머/세라믹 복합체의 유효유전상수를 예측하는데 가장 유용한 식을 찾고 BaTiO$_3$ 분말의 유전상수를 추정하고자 하였다. Lichtenecker식과 Jayasundere-Smith식이 에폭시/$BaTiO_3$ 복합 내장형 커패시터 필름의 유전상수 예측에 유용한 것으로 나타났다. 피팅을 통해 계산된 $BaTiO_3$ 분말의 유전상수는 분말의 크기에 따라 100 에서 600 사이였는데 이는 다결정 세라믹 $BaTiO_3$의 유전상수보다 작은 값이다.

• Interaction and multiscale mechanics
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• 제2권3호
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• pp.321-332
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• 2009

Recent development in composites containing phase-transforming particles, such as vanadium dioxide or barium titanate, reveals the overall stiffness and viscoelastic damping of the composites may be unbounded (Lakes et al. 2001, Jaglinski et al. 2007). Negative stiffness is induced from phase transformation predicted by the Landau phase transformation theory. Although this unbounded phenomenon is theoretically supported with the composite homogenization theory, detailed stress analyses of the composites are still lacking. In this work, we analyze the stress distribution of the Hashin-Shtrikman (HS) composite and its two-dimensional variant, namely a circular inclusion in a square plate, under the assumption that the Young's modulus of the inclusion is negative. Assumption of negative stiffness is a priori in the present analysis. For stress analysis, a closed form solution for the HS model and finite element solutions for the 2D composite are presented. A static loading condition is adopted to estimate the effective modulus of the composites by the ratio of stress to average strain on the loading edges. It is found that the interfacial stresses between the circular inclusion and matrix increase dramatically when the negative stiffness is so tuned that overall stiffness is unbounded. Furthermore, it is found that stress distributions in the inclusion are not uniform, contrary to Eshelby's theorem, which states, for two-phase, infinite composites, the inclusion's stress distribution is uniform when the shape of the inclusion has higher symmetry than an ellipse. The stability of the composites is discussed from the viewpoint of deterioration of perfect interface conditions due to excessive interfacial stresses.

• 마이크로전자및패키징학회지
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• 제8권4호
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• pp.59-65
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• 2001

경화 전 상온 보관성이 우수하며 넓은 면적에 균일한 두께와 균일한 유전특성의 커패시터를 쉽게 형성할 수 있는 epoxy/$BaTiO_3$composite커패시터 필름을 제조하였다. 이 필름은 필름 형성특성과 가공성, 그리고 상온 보관성이 우수한 에폭시계 이방성 전도 필름(Anisotropic Conductive Film: ACF)용으로 개발된 레진을 기본으로 하고, 유전상수를 높이기 위한 충진제로 2종류의 $BaTiO_3$분말을 사용하였다. X선 회절을 통하여 두 분말의 결정구조와 이에 따른 유전상수의 변화를 살펴보았으며, 점포 측정을 통해 분산제의 양을 정하였다. 필름의 경화온도와 적정한 경화제의 양을 결정해주기 위해 differential scanning calorimeter (DSC)와 커패시터의 특성 분석을 통해 경화제 양에 따른 필름 및 커패시터 특성에 미치는 영향을 살펴보았다. 이 필름을 이용하여 두께 7 $\mu\textrm{m}$에서 10 nF/$\textrm{cm}^2$ (이때의 유전상수는 80)의 높은 전기용량을 가진 우수한 커패시터를 성공적으로 제작하였다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.48.2-48.2
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• 2010

The effect of additives as rare-earth in dielectric materials has been studied to meet the development trend in electronics on the miniaturization with increasing the capacitance of MLCCs (multi-layered ceramic capacitors). It was reported that the addition of rare-earth oxides in dielectrics would contribute to enhance dielectric properties and high temperature stability. Especially, dysprosium and thulium are well known to the representative elements functioned as selective substitution in barium titanate with perovskite structure. The effects of these additives on microstructure and electric properties were studied. The 0.8 mol% Dy doped $BaTiO_3$ and the 1.0 mol% Tm doped $BaTiO_3$ had the highest electric properties as optimized composition, respectively. According to the increase of rare-earth contents, the growth of abnormal grains was suppressed and pyrochlore phase was formed in more than solubility limits. Furthermore, the effect of two rare-earth elements co-doped $BaTiO_3$ on the dielectric properties and insulation resistance was investigated with different concentration. The dielectric specimens with $BaTiO_3-Dy_2O_3-Tm2O_3$ system were prepared by design of experiment for improving the electric properties and sintered at $1320^{\circ}C$ for 2h in a reducing atmosphere. The dielectric properties were evaluated from -55 to $125^{\circ}C$ (at $1KHz{\pm}10%$ and $1.0{\pm}0.2V$) and the insulation resistance was examined at 16V for 2 min. The morphology and crystallinity of the specimens were determined by microstructural and phase analysis.

• 한국세라믹학회지
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• 제30권5호
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• pp.397-403
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• 1993

Widely used dielectrics, barium titanate was promising material for ceramic capacitor. It was produced by specific formulation with various dopants-La2O3, ZrO2, SnO2, CaZrO3, CaTiO3, CaSnO3, Bi2O3, and etc.-according to demanded properties of capacitor. In this study, we would examinate the study of dielectric properties and temperatuer characteristics (T.C.) with the amount of Bi2O3. The sample was prepared with [BaTiO3]10＋[BaZrO3, SnO2, La2O3, ZrO2]10 and Bi2O3 varied from 1.0, 1.5, 2.0, 2.5 to 3.0wt%. After milling and mixing for 15hrs, each sample was dried and then pressed at 700kg/$\textrm{cm}^2$ into pellets. Pellets were fired at 131$0^{\circ}C$, for 3hrs in air. As the result of measurements, dielectric constant, break down voltage, and insulation resistance were increased with the amount of Bi2O3, and the resonant frequency was shifted from high frequency to low frequency range. In the case of temperature characteristics, capacitance change rate was symmetrically changed at -$25^{\circ}C$ and ＋85$^{\circ}C$ respectively. Therefore, it is recognized that the temperature characteristics can be moderated with doping Bi2O3 in our study.

• Transactions on Electrical and Electronic Materials
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• 제8권6호
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• pp.241-245
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• 2007

[ $(Ba_{0.9-x}Sr_xCa_{0.10})TiO_3$ ] (x=0.33, 0.36) powders were prepared by sol-gel method. $(Ba,Sr,Ca)TiO_3$(BSCT) thick films, undoped and doped with $MnCO_3$ and $Yb_2O_3(0.1{\sim}0.7mol%)$, were fabricated by the screen printing method on the alumina substrate. The coating and drying procedure was repeated 6-times. The Pt bottom electrode was screen printing method on the alumina substrate. These BSCT thick films were annealed at $1420^{\circ}C$ for 2 hr in atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at $590^{\circ}C$ for 10 min. And then the structured and dielectric properties as a function of the doping amount of $Yb_2O_3$ were studied. As a result of the TG-DTA, exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All BSCT thick films showed XRD patterns of typical cubic peroveskite structure. The average thickness of BSCT thick films was about $70^{\mu}m$. The curie temperature and the dielectric constant decreased with increasing $Yb_2O_3$ doped content and the relative dielectric constant of the specimen, doped with 0.5 mol% $Yb_2O_3$ at BSCT(54/36/10), showed a best value of 5018 at curie temperature.

• 한국세라믹학회지
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• 제33권2호
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• pp.228-234
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• 1996

강유전성 BaTiO3의 분역 구조를 이해하는 것은 폴링과정에 있어서 대단히 중요하면 대부분의 BaTiO3 세라믹스에서 흔히 발견되는 구조 쌍정 계면에서의 배향관계는 아직까지 보고된 바 없다. 본 연구에서는 {111} 쌍정을 이루고 있는 길정시편을 이용하여 편광현미경하에서 분역구조를 관찰하고, 열처리에 의하여 상전이되는 동안 {111} 쌍정과 강유전성 분역의 거동을 현미경하에서 직접적으로 관찰하였다. {111} 쌍정면 암측으로 대칭적 분역구조가 발될되며, 그 배열 형태는 'V'자 모양과 수직하게 관통하는 것처럼 직선 모양의 두가지 형으로 분류된다. 열처리에 의하여 새로운 분역구조가 형성될때 {111} 쌍정면 주위에서는 대칭적 관계를 유지하면서 분역이 발달되며, 분역형성에 기인하는 표면변형도 {111} 쌍정에 대하여 항상 대칭적으로 발달된다. 이는 {111} 계면에서도 분극반향이 바뀌어지며 "머리-꼬리"의 전지적 안정성의 배향관계를 유지하는 것으로 설명할 수 있다.