• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.323-324
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• 2006

저온동시 소결용 세라믹스, LTCC를 사용한 RF/MW용 고유전율 세라믹을 개발하기 위하여 300이상의 고유전율과 낮은 손실 계수를 가지는 것으로 알려진 $Ag(Nb_{1/4}Ta_{3/4})O_3$ 고용체와 $CaTiO_3$, $TiO_2$를 각각 혼합하여 공진주파수의 온도 계수가 0에 가까운 안정된 유전체 특성을 얻고자 하였다. 유전율의 온도 안정성을 도모하기 위해 음의 온도 계수를 갖는 $CaTiO_3$, $TiO_2$와 양의 온도계수를 갖는 $CaTiO_3$ 및 $TiO_2$를 일정 분율로 혼합한 복합체 구조의 시편을 제작하였다. LTCC 소자로의 적용을 위해 3wt.%의 CuO를 첨가하여 소결 온도를 낮추었으며, 소결 시편의 상 분석, 미세구조 및 전기적 특성을 조사하였다.

• 한국세라믹학회지
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• 제40권4호
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• pp.340-345
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• 2003

B $i_2$ $O_3$-Ti $O_2$ composite dielectric ceramics have been prepared by a conventional solid state ceramic route. The composite ceramics were prepared with starting materials of different origin and the microwave dielectric properties were investigated. The sintered ceramics were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, Raman and microwave methods. Structural and microstructural analyses identified two separate phases: Ti $O_2$(rutile) and B $i_2$ $Ti_4$0$_{11}$. The separate grains of titania and bismuth titanate were distributed uniformly in the ceramic matrix. The composition 0.88Ti $O_2$-0.12B $i_2$ $Ti_4$ $O_{11}$ was found to have a Q$\times$f of 9300 GHz (measured at a frequency of 3.9 GHz), a temperature coefficient of frequency, $\tau$$_{cf}$ near zero and a high relative permittivity, $\varepsilon$r of 83. The microwave dielectric properties were measured down to 20$^{\circ}$K K. The quality factor increased on cooling the ceramic samples.les.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1992년도 춘계학술대회 논문집
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• pp.137-139
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• 1992

By addition of 1～5mol% CeO$_2$to powders with composition in the BaO-Nd$_2$O$_3$-TiO$_2$, temperature coefficient of permittivity of sintered ceramics may be decreased from approximately-140ppm/$^{\circ}C$～-65ppm/$^{\circ}C$. Dense, fine grained ceramics were prepared with permitivity within the range of 78～92 and Q above 1000.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1992년도 추계학술대회 논문집
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• pp.59-62
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• 1992

In this study, $TiO_2$ thin films are fabricated by Sol-Gel method and dielectric, electric and humidity sensing properties have been investigated. The structure of Sol can be changed by controlling for hydrolysis reaction condition. The uniformity of the surface on $TiO_2$ thin films is confirmed by SEM. The permittivity of $TiO_2$ thin films increases according to heat treatment temperature, whereas the conductivity of $TiO_2$ thin films decreases according to heat treatment temperature, As the results of measuring humidity sensing properties of $TiO_2$ thin films fabricated as humidity sensor, it is confirmed to have good humidity sensing properties in high humidity and low frequency.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.297-297
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• 2007

The $(B_{0.5},Sr_{0.5})TiO_3$ ceramics, which added with low sintering materials $Li_2CO_3$ and ZnBO, was investigated for LTCC(low temperature co-fired ceramic) applications. To compare sintering temperature of $(B_{0.5},Sr_{0.5})TiO_3$ respectively, we added 1, 2, 3, 4, and 5wt% of $Li_2CO_3$ and ZnBO to $(B_{0.5},Sr_{0.5})TiO_3$. For confirming the sintering temperature, the respective specimens were sintered from $750^{\circ}C$ to $1200^{\circ}C$ by $50^{\circ}C$. The case of $Li_2CO_3$ greatly lowered the sintering temperature of $(B_{0.5},Sr_{0.5})TiO_3$ ($1350^{\circ}C$) below $900^{\circ}C$. The addition of ZnBO improved the loss tangent of $(B_{0.5},Sr_{0.5})TiO_3$. The crystalline structure of $LiCO_3$ doped $(B_{0.5},Sr_{0.5})TiO_3$ and ZnBO doped $(B_{0.5},Sr_{0.5})TiO_3$ was analyzed with the X-ray diffraction (XRD) analysis. The dielectric permittivity and loss tangent of $Li_2CO_3$ doped BST and ZnBO doped BST were measured with the HP 4284A precision. From the electrical characterization, we respectively obtained the dielectric permittivity 1361, loss tangent $6.94{\times}10^{-3}$ at $Li_2CO_3$ doped $(B_{0.5},Sr_{0.5})TiO_3$ (3wt%) and the dielectric constant 1180, loss tangent $3.70{\times}10^{-3}$ at ZnBO doped $(B_{0.5},Sr_{0.5})TiO_3$(5wt%).

• The Korean Journal of Ceramics
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• 제1권1호
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• pp.13-20
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• 1995

Effects of thermal annealing on the dielectric/piezoelectric properties of $Pb(Zn, Mg)_{1/3}Nb_{2/3}O_3-PbTiO_3$ ceramics (PZMNPT) with Zn/Mg=6/4) were examined across the rhombohedral/tetragonal morphotropic phase boundary (MPB). Both the relative dielectric permittivity ($\varepsilon$r)and the piezoelectric constant($d_33$)/electromechanical coupling constant ($k_p$)were increased by thermal annealing ($800^{\circ}$~$900^{\circ}C$) after sintering at $1150^{\circ}C$ for 1 hr. Based on the dielectric analysis using the series mixing model and the concept of a random distribution of the local Curie points, the observed improvements in the dielectric and piezoelectric properties of PZMN-PT were interpreted in terms of the elimination of PbO-rich amorphous intergranular layers(~1nm) induced by thermal annealing. A concrete evidence of the presence of amorphous grain-boundary layers in the unannealed (as-sintered) specimen was obtained by examining the structure of intergranular region using a TEM.

• 한국재료학회지
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• 제13권4호
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• pp.259-265
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• 2003

For the aim of thin microwave absorbers used in mobile telecommunication frequency band, this study proposed a high permittivity dielectrics(λ/4 spacer) coated with ITO thin films of 377 $\Omega$/sq(impedance transformer). High frequency dielectric properties of ferroelectric ceramics, electrical properties of ITO thin films and microwave absorbing properties of ITO/dielectrics were investigated. Ferroelectric materials including $BaTiO_3$(BT), 0.9Pb($Mg_{1}$3/Nb$_{2}$3/)$O_3$-0.1 $PbTiO_3$(PMN-PT), 0.8 Pb (Mg$_{1}$3/$Nb_{2}$3/)$O_3$-0.2 Pb($Zn_{1}$3$_Nb{2}$3/)$O_3$(PMN-PZN) were prepared by ceramic processing for high permittivity dielectrics,. The ferroelectric materials show high dielectric constant and dielectric loss in the microwave frequency range. The microwave absorbance (at 2 ㎓) of BT, 0.9PMN-0.1PT, and 0.8PMN-0.2PZN were found to be 60%(at a thickness of 3.5 mm), 20% (2.5 mm), and 30% (2.5 mm), respectively. By coating the ITO thin films on the ferroelectric substrates with λ/4 thickness, the microwave absorbance is greatly improved. Particularly, when the surface resistance of ITO films is closed of 377 $\Omega$/sq, the reflection loss is reduced to -20 ㏈(99% absorbance). This is attributed to the wave impedance matching controlled by ITO thin films at a given thickness of high permittivity dielectrics of λ/4 (3.5 mm for BT, 2.5 mm for PMN-PT and PMN-PZN at 2 ㎓). It is, therefore, successfully proposed that the ITO/ferroelectric materials with controlled surface resistance and high dielectric constant can be useful as a thin microwave absorbers in mobile telecommunication frequency band.

• 대한화학회지
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• 제53권1호
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• pp.42-50
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• 2009

유전율-분광법과 교류 전도도 측정 연구를 망간이 혼입된 층상구조의 $Na_{1.9}Li_{0.1}Ti_3O_7$에 시도하였다. 373-723K 온도와 100Hz-1MHz 주파수 영역에서 loss 탄젠트 (Tan$\delta$), 상대적 유전율 ($\varepsilon_{r}$) 그리고 교류 전도 도 ($\sigma_{ac}$)의 의존성을 혼입 유도체들에 대하여 조사하였다. 다양한 전도도 메커니즘이 존재하는데 MSLT-1과 MSLT-2의 경우에는 낮은 온도영역에서 전자에 의한 전도도를 보인다. MSLT-3의 경우에는 금지된 층간 이온 전 도도가 전자 전도도와 함께 존재한다. 이러한 층간 이온 전도도는 모든 혼입 유도체들에 대하여 중간 온도 영역에 존재한다. 가장 높은 온도 영역에서는 MSLT-1과 MSLT-2의 경우에는 이온 전도도와 polaron에 의한 전도도가 존재하고 MSLT-3에 대하여는 이온 전도도 만이 존재한다. 망간이 혼입된 층상구조의 $Na_{1.9}Li_{0.1}Ti_3O_7$에서 Loss 탄젠트 (Tan$\delta$)는 전자 전도도와 쌍극자의 위치, 그리고 공간 전하 분극화에 기인한다. 상대적 유전율의 증가는 층간 에 쌍극자 수의 증가에 기인하고 반면 상대적 유전율의 감소는 높은 혼입율에 따른 누전 전류의 증가에 기인한다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.234-234
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• 2008

Chemically homogeneous $Ba_{0.6}Sr_{0.4}TiO_3$ (BST) sols were synthesized using barium acetate, strontium acetate, and titanium isoproxide as starting materials. BST thin films of thickness 340 nm were deposited on Pt/$TiO_2/SiO_2$/Si and alumina substrates using spin coating method. The technique used for the processing of these films was Ultraviolet (UV) sol-gel photoannealing, using phto-sensitivity precursor solutions and UV-assisted rapid thermal processing(UV-RTP). The crystallization behaviour of the BST sols and thin films was studied by differential thermal analysis (DTA) and X-ray diffraction (XRD). Variation of permittivity and dielectric loss were measured in LCR-meter, model HP 4394A.

• 한국세라믹학회지
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• 제40권4호
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• pp.371-374
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• 2003

Various types of equation for mixing rule on permittivity of mixture have been proposed, but none of these is not perfect because of the inconsistency between the actual geometrical configuration and the basic model for calculation. Serial model and parallel model are lower and upper extremes of mixing manner, the apparent permittivity of any other type of mixture stay between these two extreme states. For the random mixture of the stumpy fine particles, customarily the logarithmic mixing rule has been applied. But, the logarithmic mixing rule does not give the proper value of permittivity in low or high mixing rate of constituent. The author proposed the new mixing rule that gives better consistency with measured value in whole mixing range compared to the logarithmic rule. In this paper, a desirable refinement on the equation proposed in the previous paper is made to adapt to thr configuration image of actual compound and then the equation has been expanded to the complex permittivity to apply the mixing rule on the dissipative materials cases.