• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.334-345
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• 2008

컴퓨터의 발달과 더불어 현대사회는 기록하고 보존해야할 정보의 양이 점점 방대해 지고 있다. 그로 인해 자기기록매체처럼 정보를 사용자의 편의에 따라 반복적으로 기록하고 재생할 수 있는 광기록매체에 대한 관심이 증가되고 있다. $Ge_2Sb_2Te_5$(GST)는 기존의 CD-RW나 Floppy Disk(FD)를 대체할 차세대 기록매체로 주목받고 있다. 따라서 본 연구에서는 비정질상과 결정상으로 변하는 성질을 가지고 있는 GST롤 상변화 기록매체로서 이용하기 위해 굴절률을 평가하였다. 시료는 5N의 순도를 갖는 Ge, Sb, Te 물질을 준비하고 조성비에 맞추어서 석영관에 진공 봉입한 후 용융-냉각법으로 벌크를 제작하였고 열증착 방법으로 Si 및 유리 기판위에 1000nm 두께로 박막을 제작하였다. UV-Vis-IR spectrophotometer를 사용하여 반사도와 투과도를 측정하였고 측정한 스펙트럼을 이용하여 Swanepoel method로 굴절률을 계산하였다. 본 연구진이 자체 개발한 계산툴에 실험값을 대입하였고 실험에 의해 얻은 투과도와 계산툴에 의해 얻은 투과도 스펙트럼을 비교하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.2
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• pp.86-90
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• 2017

This work reports the phase-change behavior and thermal stability of doped GeSbTe/GeSbTe bilayers. We prepared the bilayers using RF sputtering, and annealed them at annealing temperature ranging from $100^{\circ}C$ to $400^{\circ}C$. The sheet resistance of the bilayer decreased and saturated with increasing annealing temperature, and the saturated value was close to that of pure GeSbTe film. The surface of the bilayer roughened at $400^{\circ}C$, which corresponds to the surface roughening of doped GeSbTe film. Mixed phases of face-centered cubic and hexagonal close-packed crystalline structures were identified in the bilayers annealed at elevated temperature. These results indicate that the phase-change behavior of the bilayer depends on the concurrent phase-transitions of the two GeSbTe-based films. The dopants in the doped GeSbTe film were diffused out at annealing temperatures of $300^{\circ}C$ or higher, which implies that the thermal stability of the bilayer should be considered for its application in phase-change electronic devices.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.7
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• pp.408-413
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• 2016

The dielectric thin films applied to multi-colored semitransparent thin film solar cells have been extensively studied. In this work, we prepared GeSbTe and GeTe chalcogenide thin films using magnetron sputtering, and investigated their optical and phase-change properties to replace the dielectric films. The changes of surface morphology, sheet resistance, and X-ray diffraction of the Te-based chalcogenide films support the fact that the amorphous stability of GeTe films is superior to that of GeSbTe films. While both amorphous GeSbTe and GeTe films thinner than 30 nm have optical transparency between 5% and 60%, GeTe films transmit more visible light than GeSbTe films. It is confirmed by computer simulation that the color of semitransparent silicon thin film solar cells can be adjusted with the addition of GeSbTe or GeTe films. Since it is possible to adjust the contrast of the solar cells by exploiting the phase-change property, the two kinds of chalcogenide films are anticipated to be used as an optical layer in semitransparent solar cells.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05a
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• pp.42-45
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• 2003

The phase transformation of $REBa_2Cu_3O_{7-x}$ (RE=Nd, Gd, Dy) was investigated using isothermal heat-treatment and continuous cooling in air. During continuous cooling, the $REBa_2Cu_3O_{7-x}$ (RE=123) superconducting phase with well-distributed $REBa_2Cu_3O_{7-x}$ (RE-211) was obtainde at a cooling rate of $0.001^{\circ}C$/s. Single phase RE-123 (Nd, Gd, Dy) was stable at $1050^{\circ}C$, $1050^{\circ}C$, and $950^{\circ}C$ during isothermal heat-treatment, respectively. Above these temperatures the RE-211 phase existed within the RE-123 grains. The RE-123, RE-211, $BaCu_2Od_2$, and CuO phases coexisted at $50^{\circ}C$ below the partial melting temperature for each respective rare-earth RE-123.

• Korean Journal of Materials Research
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• v.12 no.5
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• pp.375-381
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• 2002

N-type ${\beta}-FeSi_2$ with a nominal composition of $Fe_{0.98}Co_{0.02}Si_2$ powders has been produced by mechanical alloying process and consolidated by vacuum hot pressing. As-milled powders were of metastable state and fully transformed to ${\beta}-FeSi_2$ phase by subsequent isothermal annealing. However, as-consolidated $Fe_{0.98}Co_{0.02}Si_2$ consisted of untransformed mixture of ${\alpha}-Fe_2Si_ 5$ and $\varepsilon$-FeSi phases. Isothermal annealing has been carried out to induce the transformation to a thermoelectric semiconducting ${\beta}-FeSi_2$ phase. The transformation behavior of ${\beta}-FeSi_2$ was investigated by utilizing DTA, a modified TGA under magnetic field, SEM, and XRD analyses. Isothermal annealing at $830^{\circ}C$ in vacuum led to the thermoelectric semiconducting ${\beta}-FeSi_2$ phase transformation, but some residual metallic $\alpha$ and $\varepsilon$ phases were unavoidable even after prolonged annealing. Thermoelectric properties were remarkably improved by isothermal annealing due to the transformation from metallic $\alpha$ and $\varepsilon$ phases to semiconducting phases.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.5
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• pp.411-414
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• 2008

The germanium films were deposited by metal organic chemical vapor deposition using $Ge(allyl)_4$ precursors on TiAlN substrates. Deposition of germanium films was only possible with a presence of $Sb(iPr)_3$, which means that $Sb(iPr)_3$ takes a catalytic role by a thermal decomposition of $Sb(iPr)_3$ for Ge film deposition. Also, as Sb bubbler temperature increases, deposition rate of the Ge films increases at a substrate temperature of $370^{\circ}C$. The GeTe thin films were fabricated by MOCVD with $Te(tBu)_2$ on Ge thin film. The GeTe films were grown by the tellurium deposition at $230-250^{\circ}C$ on Ge films deposited on TiAlN electrode in the presence of Sb at $370^{\circ}C$. The GeTe film growth on Ge films depends on the both the tellurium deposition temperature and deposition time. Also, using $Sb(iPr)_3$ precursor, GeSbTe films with hexagonal structures were fabricated on GeTe thin films. GeSbTe films were deposited in trench structure with 200 nm*120 nm small size.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.304-304
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• 2007

고주파 모률에서 사용되는 기판소재는 저유전율과 낮은 loss 특성을 요구함으로 지속적인 연구를 필요로 한다. 지금까지의 ceramic/glass composite 에서 주로 사용된 ceramic filler는 Al2O3로 낮은 유전률을 구현에 한계가 있었다. Cordierite는 낮은 유전율 (${\varepsilon}_r$ < 4)을 나타내는 filler로서 그 가능성이 높지만 아직까지 보고된 결과들이 미흡한 실정이다. 따라서 본 연구에서는 cordierite filler와 SiO2-B2O3-Al2O3-RO (R : Zn, Sr, Ba, Ca)계의 glass를 혼합하여 LTCC용 기판소재로서의 가능성을 확인하고자 저온 동시소성이 가능한 소결온도인 $850^{\circ}C{\sim}1.000^{\circ}C$ 사이에서 소재의 소결실험을 진행하였다. 소결온도에 따른 상변화, 유전특성을 확인한 결과 filler로 사용된 cordierite상만이 관찰 되었으며 소결조건에 따라 5.0~5.5의 낮은 유전율과 1.000~1,500의 Q를 나타내는 것을 확인 하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.118-119
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• 2005

PRAM (Phase Change Random Access Memory) is well known to use reversible phase transition between amorphous (high resistance) and crystalline (low resistance) states of chalcogenide thin film by electrical Joule heating. In this paper, we introduce a stack-type PRAM device with a novel GST/TiAlN structures (GST and a heating layer of TiAlN), and report its electrical switching properties. XRD analysis result of GST thin film indicates that the crystallization of the GST film start at about $200^{\circ}C$. Electrical property results such as I-V & R-V show that the phase change switching operation between set and reset states is observed, as various input electrical sources are applied.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.118-119
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• 2006

In the present work, we investigate the basic physical and thermal properties and electrical resistance change due to phase change in chalcogenide-based $Ge_1Se_1Te_2$ and $Ge_2Se_2Te_5$ thin films. The phase transition from amorphous to crystalline states, and vice versa, of $Ge_1Se_1Te_2$ and $Ge_2Se_2Te_5$ thin films by applying electrical pulses have been studied. The reversible phase transition between the amorphous and crystalline states, which is accompanied by a considerable change in electrical resistivity, is exploited as means to store bits of information.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.280-281
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• 2006

Cordierite 결정상을 LTCC공정 적용온도에서 소결하기 위한 glass 조성을 조사하였다. 상용의 glass중 Pb-B-Si-O계, Na-Zn-B-O계 glass를 선택하였고 LTCC용 기판소재로서의 가능성을 확인하기 위하여 저온 동시소성이 가능한 소결온도인 $850^{\circ}C$와 $1000^{\circ}C$ 사이에서 소재의 소결실험을 진행하였다. 소결조건에 따른 상변화, 유전특성을 확인한 결과 glass상, 결정상, 용융에 의한 glass상으로 상의 변화가 있음을 확인 할 수 있었으며, LTCC 소결 조건에서 Pb-B-Si-O계 glass의 경우 2.9~3.7의 낮은 유전율과 0.0027의 우수한 dielectric loss, 내전압 특성을 가지고 있음을 확인하였다.