• Proceedings of the Materials Research Society of Korea Conference
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• 2005.05a
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• pp.250-250
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• 2005

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.272-273
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• 2006

LTCC(low temperature co-fired ceramics)용 glass/ceramic 복합체를 제조하기 위해 4 종류의 borosilicate계 glass를 선정하고 filler로 $Al_2O_3$ ceramics를 filler 사용하여 30~50 vol% glass frit에 따른 소결 및 유전 특성에 대하여 조사하였다. Glass frit은 $SiO_2$와 $B_2O_3$ 함량비를 고정한 후 R(CaO, BaO, ZnO, $Bi_2O_3$)에 따라 유리 연화온도(Ts)와 함량이 소결에 미치는 영향 및 유전 특성 변화를 고찰한 결과, CaO-$B_2O_3-SiO_2$ glass의 경우 다량의 2 차상이 형성되었고, 이에 $900^{\circ}C$ 이하에서 완전 소결이 이루어지지 않았으며, BaO-$B_2O_3-SiO_2$ glass는 celsian($BaAl_2Si_2O_8$) 결정이 형성되면서 소결성의 저하를 갖고 왔으며, ZnO-$B_2O_3-SiO_2$ glass는 소결이 진행됨에 따라 주상이 $Al_2O_3$에서 gahnite($ZnAl_2O_4$) 결정이 형성되면서 품질계수가 크게 증가하였으며, $Bi_2O_3-B_2O_3-SiO_2$ glass는 45 vol%일 때 $900^{\circ}C$에서부터 일정한 선수축율 특성을 나타내었지만, 다량의 액상으로 인하여 유전 특성의 저하를 나타내었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.741-742
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• 2011

XRD 결과와 TEM 분석으로부터 열처리효과에 따른 Bi-Te 박막의 미세구조 변화를 확인하였다. $Bi_2Te_3$ 상이 $SiO_2$ 와 Bi-Te 박막의 경계면을 따라서 성장하였고 이는 열전성능에 중요한 영향을 미치는 것을 확인하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.11
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• pp.1048-1055
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• 2005

The formula to calculate a variation of optical path length of single crystal by the electric field was derived by this study. The formula was applied to $Bi_{12}SiO_{20}$ single crystal. The results are as follows. In case of the applied electric field in the body diagonal direction and the passing light along the same direction, the variation of optical path length had the largest value. The symmetry of the space distribution of optical path length satisfied $E3C_2\;8C_3$, the set of elements of the symmetry of $Bi_{12}SiO_{20}$ single crystal. The property which gave the largest influence to the variation of optical path length is the strain of length by the Inverse piezoelectric effect. The second influence, is the variation of the refractive index by the electro-optic effect. The variation of optical path length by the inverse piezoelectric effect and by the electro-optic effect have a reverse sign each other.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.233-239
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• 2000

Sr0.9Bi2+xTa2O9(x=0, 0.1, 0.2, 0.3) thin films on IrO2/SiO2/Si or Pt/Ti/SiO2/Si substrate were prepared by spin coating method using SBT stock solutions synthesized by MOD process. SBT thin films on IrO2 transformed to layered perovskite phase at $700^{\circ}C$, but showed low breakdown voltage due to their porous microstructure. The smaple of Sr0.9Bi2+xTa2O9 composition showed the best dielectric and electrical properties. When the sample of the same composition was annealed at 80$0^{\circ}C$, the dielectric and electric properties were improved due to the grian growth and dense surface. the remanent polarization values(2Pr) at $\pm$3 V for IrO2 and Pt electrodes were 10.5, 7.15$\mu$C/$\textrm{cm}^2$, respectively. The SBT thin film with IrO2 electrode showed the lower coercive field. The leakage current density and breakdown voltage of SBT thin films on IrO2 were higher than those on Pt.

• Journal of the Korean Magnetics Society
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• v.20 no.6
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• pp.222-227
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• 2010

$BiFeO_3$ (BFO) thin films were deposited on Pt/Ti/$SiO_2$/Si(100) substrates by RF magnetron sputtering method at room temperature. The influence of the flow rate of $O_2$ gas on the preparation of $BiFeO_3$ thin films was studied. XRD results indicate that the $BiFeO_3$ thin films were crystallized to the perovskite structure with the presence of small amount of impurity phases. The flow rate of $O_2$ gas has great affect on the microstructures and magnetic properties of $BiFeO_3$ thin films. As flow rate of $O_2$ gas increased, roughness and grain size of the thin films increased. $BiFeO_3$ thin films exhibited weak ferromagnetic behavior at room temperature. The PFM images revealed correlation between the surface morphology and the piezoresponse, indicating that the piezoelectric coefficient is related to microstructure.

• Current Optics and Photonics
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• v.1 no.6
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• pp.613-617
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• 2017

Due to optimal advances such as chromatic performance, durability, low power consumption, high efficiency, long-lifetime, and excellent environmental friendliness, white LEDs (WLEDs) are widely used in vehicle front lighting, backlighting, decorative lighting, street lighting, and even general lighting. In this paper, the remote packaging WLEDs (RP-WLEDs) with bi-layer red-emitting $Sr_2Si_5N_8:Eu^{2+}$ and yellow-emitting YAG:Ce phosphor was proposed and investigated. The simulation results based on the MATLAB software and the commercial software Light Tools indicated that the color rendering index (CRI) of bi-layer phosphor RP-WLEDs had a significant increase. The CRI had a considerable increase from 72 to 94. In conclusion, the results showed that bi-layer red-emitting $Sr_2Si_5N_8:Eu^{2+}$ and yellow-emitting YAG:Ce phosphor could be a prospective approach for manufacturing RP-WLEDs with enhanced optical properties.

• Korean Journal of Crystallography
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• v.11 no.2
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• pp.95-101
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• 2000

Ferroelectric SrBi2Ta2O9 (SBT) thin films of Pt/Ti/SiO2 electrode were fabricated using a sintered SBT target with various Bi2O3 content by rf magnetron sputtering. Good hysteresis loop characteristics were observed in the SBT thin films deposited with 50mol% excess Bi target. SBT thin films crystallized from 650℃ however, good hysteresis loop can be obtained in the film annealed above 700℃. pt/TiO2/SiO2 and Pt/SiO2 electrodes were also used to investigate the Pt electrode dependence of SBT thin films. SBT thin films showed random oriented polycrystalline structure and similar morphology regardless of electrodes with quite different surface morphology. A 0.2㎛ thick SBT film annealed at 750℃ exhibited the remanent polarization (2Pr) of μC/㎠ and coercive voltage(Vc) of 1V at an applied voltage of 5V.

• Journal of the Korean Ceramic Society
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• v.37 no.10
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• pp.1008-1013
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• 2000

SrTi $O_3$(001) 단결정 기판 위에 졸-겔 스핀코팅으로 $SrBi_2(Ta,Nb)_2O_9$ 박막을 도포하고 그 결정화 과정을 고온 X-선 회절분석 (HTXRD)으로 추적하면서 Pt(111)/Ti/ $SiO_2$/Si 위에 성장한 박막과 비교하였다. SrTi $O_3$(001) 단결정 기판 위에 도포된 $SrBi_2Nb_2O_{9}$ 박막은 fluorite-like phase와 같은 transient phase를 거치지 않고 곧바로 순수한 $SrBi_2Nb_2O_9$ 상으로 결정화가 시작되었으며 결정화가 시작되는 온도인 ${\sim}540^{\circ}C$부터 c축 배향성장하였다. 또한 $SrB i_2(Ta,Nb)_2O_9$ 박막은 Ta/Nb 비에 관계없이 $SrTiO_3$(001) 위에서 모두 $(00{\ell})$로 배향되었으며, 코팅 횟수가 늘어나 필름의 두께가 증가함에 따라 c축 배향성은 미세한 감소를 보였다. $SrBi_2Nb_2O_9/SrTiO_3$단면을 TEM으로 관찰한 결과 $SrBi_2Nb_2O_9$은 대체로 불규칙한 크기의 다결정체로 되어 있었으나 계면 부근에서는 [001]$_{SBN}$//[001]$_{SrTi}$ $O_3$/, [100]$_{SBN}$//[100]$_{SrTi}$ $O_3$/라는 결정학적 관계를 가지며 에피탁샬 성장했음을 알 수 있었다.있었다.

• Journal of the Korean Ceramic Society
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• v.34 no.8
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• pp.897-907
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• 1997

Thin films of Bi4-xSmxTi3O12(0$\leq$x$\leq$2) were prepared on Pt/Ti/SiO2/Si(100) at $700^{\circ}C$ using spin-coating with sols derived from Bi-Sm-Ti complex alkoxides. From X-ray diffraction analysis, it was observed that Sm-substituted phases resembled ferroelectric Bi4Ti3O12 in structure. Variations of their lattice parameters depending on the amount of Sm-substitution showed that an anomalous structural distortion might exist at x=1. The grain sizes of the thin films decreased from 0.115 ${\mu}{\textrm}{m}$ to 0.078${\mu}{\textrm}{m}$ with increasing the amount of Sm-substitution. The dielectric constants and the remanent polarizations of the thin films decreased with increasing the amount of the Sm-substitution, which were related to decrease of the stereo-active Bi3+ ion contributing to polarization. However, these values were exceptionally high at x=1, compared to those of the other substituted phases. Such an anomaly suggests that the phase of x=1 has 1:1 chemical ordering between Sm and Bi in structure. The thin films of all compositions except x=2 showed ferroelectricity. The thin film of x=2 was paraelectric, whose grains were too fine to exhibit ferroelectricity.