• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.218.1-218.1
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• 2013

GeSbTe 삼원계 칼코겐화물 합금은 광디스크 및 상변화 메모리에서 활성물질로 사용되는 대표적인 재료이다. GeSbTe 합금은 결정질 상과 비정질 상의 두 종류의 상을 갖는데 그 상에 따라 반사율 및 전기저항이 서로 다르기 때문에 활성물질로서 작용한다. GeSbTe 합금 구성원소의 일부를 포함하는 두 종류의 물질로 접합을 형성하고 열처리 공정을 수행함으로써 GeSbTe 합금을 국부적으로 생성하는 방법이 최근에 보고되었다. 이러한 방법을 상변화 메모리 소자 제조에 이용하면 GeSbTe 합금을 제한된 영역에 나노 스케일로 만드는 것이 가능해져서 GeSbTe 합금의 상변화를 유도하는데 필요한 프로그래밍 전류를 낮추는 효과를 얻을 수 있다. 상변화 메모리 소자 내에서의 GeSbTe 합금의 두께 또는 크기는 상변화 메모리 소자의 동작 특성을 좌우하는 중요한 파라미터이며 이것은 열처리 공정 조건에 따라 결정되므로 열처리 공정 조건에 따라 GeSbTe 합금이 생성되는 양상이 어떻게 변화하는지를 밝힐 필요가 있다. 따라서 본 연구에서는 다양한 열처리 온도 조건에서 Ge-Sb-Te 삼성 분계에서의 구성 원소들의 상호확산 거동을 조사하였다. 순수한 Ge 박막과 조성이 다른 SbTe 박막의 접합을 형성하고 773K까지의 온도 범위에서 열처리를 실시하였다. Auger 수직 분석을 이용하여 Ge, Sb, 및 Te 원소의 깊이 방향의 확산 정도를 조사하였으며 그 결과로서 열처리 온도가 증가함에 따라 상호확산 정도가 심해지고 Te 원소가 상호확산에 있어서 중요한 역할을 한다는 사실을 확인하였다.

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.3
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• pp.144-147
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• 2017

In this study, $Ge_2Sb_2Te_5$ and $Ge_8Sb_2Te_{11}$ were used as an insulator layer to fabricate ReRAM devices. The resistance change is correlated to the appearance or disappearance of a conductivity filament at the surface of the GeSbTe layer. Changes in the electrical properties of ITO/GeSbTe/Ag devices were measured using a I-V-L measurement system. As a result, compared to the $ITO/Ge_8Sb_2Te_{11}/Ag$ device, this $ITO/Ge_2Sb_2Te_5/Ag$ ReRAM device exhibits highly uniform bipolar resistive switching characteristics, such as the operating voltages, and the resistance values.

• 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.35 no.1
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• pp.44-49
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• 2022

In this paper, we investigated current (I)- and voltage (V)-sweeping properties in a double-stack structure, Ge₂Sb₂Te₅/Ti/W-doped Ge₈Sb₂Te₁₁, a candidate medium for applications to multilevel phase-change memory. 200-nm-thick and W-doped Ge₂Sb₂Te₅ and W-doped Ge₈Sb₂Te₁₁ films were deposited on p-type Si(100) substrate using magnetron sputtering system, and the sheet resistance was measured using 4 point-probe method. The sheet resistance of amorphous-phase W-doped Ge₈Sb₂Te₁₁ film was about 1 order larger than that of Ge₂Sb₂Te₅ film. The I- and V-sweeping properties were measured using sourcemeter, pulse generator, and digital multimeter. The speed of amorphous-to-multilevel crystallization was evaluated from a graph of resistance vs. pulse duration (t) at a fixed applied voltage (12 V). All the double-stack cells exhibited a two-step phase change process with the multilevel memory states of high-middle-low resistance (HR-MR-LR). In particular, the stable MR state is required to guarantee the reliability of the multilevel phase-change memory. For the Ge₂Sb₂Te₅ (150 nm)/Ti (20 nm)/W-Ge₈Sb₂Te₁₁ (50 nm), the phase transformations of HR→MR and MR→LR were observed at t<30ns and t<65ns, respectively. We believe that a high speed and stable multilevel phase-change memory can be optimized by the double-stack structure of proper Ge-Sb-Te films separated by a barrier metal (Ti).

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.215-222
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• 2002

Using an in-situ ellipsometer, we monitored the growth curve of optical recording media in real time. For confirmation of the thickness control using in-situ ellipsometry, we analyzed the deposited multi-layer sample made of Ge-Sb-Te alloy film and ZnS-Si0$_2$ dielectric films using an exsitu spectroscopic ellipsometer. The target material in the first sputtering gun is ZnS-SiO$_2$ as the protecting dielectric layer and that in the second gun is Ge$_2$sb$_2$Te$_{5}$ as the receding layer. While depositing ZnS-SiO$_2$, Ge$_2$Sb$_2$Te$_{5}$ and ZnS-SiO$_2$ films on c-Si substrate in sequence, we measured Ψ $\Delta$ in real time. Utilizing the complex refractive indices of Ge$_2$Sb$_2$Te$_{5}$ and ZnS-SiO$_2$ obtained from the analysis of spectroscopic ellipsometry data, the evolution of ellipsometric constants Ψ, $\Delta$ with thickness is calculated. By comparing the calculated evolution curve of ellipsometric constants with the measured one, and by analyzing the effect of density variation of the Ge$_2$Sb$_2$Te$_{5}$ recording layer on ellipsometric constants with thickness, we precisely monitored the growth rate of the Ge-Sb-Te multilayer and controlled the growth process. The deviation of the real thicknesses of Ge-Sb-Te multilayer obtained under the strict monitoring is post confirmed to be less than 1.5% from the target structure of ZnS-SiO$_2$(1400 $\AA$)IGST(200 $\AA$)$\mid$ZnS-SiO$_2$(200$\AA$).(200$\AA$).

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.297.1-297.1
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• 2014

칼코겐화합물은 주기율표 6족에서 산소를 제외한 칼코겐 원소가 하나 이상 포함되는 화합물 반도체 소재로 상변화 및 광전변환 특성을 가지고 있다. 이와 같은 칼코겐화합물의 장점을 이용하여 집적회로의 로직 블록 간의 신호 전달을 제어하는 프로그래머블 스위치를 구현 할 수 있다. 본 연구에서는 프로그래머블 스위치에 적용 가능한 칼코겐화합물로 널리 알려진 GeSbTe 및 GeTe 박막의 도핑에 따른 전기적, 구조적 특성 변화를 보고한다. RF magnetron sputtering 방식을 이용하여 doped GST 및 doped GeTe 박막을 증착하고 도핑에 따른 전기적, 구조적 특성을 관찰하였다. GST 박막의 경우 도핑에 의해 면저항 값이 증가하고 결정화 온도가 상승하는 것을 확인하였다. 반면 GeTe 박막에서는 도핑에 의해 면저항 값이 감소하고 결정화 온도가 낮아지는 것을 확인하였다. 이러한 결과로부터 GeSbTe 및 GeTe 박막의 전기적 특성은 도핑에 따라 변화하며, 도핑 조건을 적절히 조절함으로써 프로그래머블 스위치에 적용 가능한 칼코겐화합물의 확보가 가능하다는 결론을 내릴 수 있다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1260_1261
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• 2009

A detailed investigation and structure of tested samples are clearly presented. As a reference, $Ge_1Se_1Te_2$/Sb only sample was also investigated. We used compound of Ge-Se-Te material for phase-change cell. Actually, the performance properties have been improved surprisingly then conventional Ge-Sb-Te. However, crystallization time was as long as ever for amorphization time. We conducted this esperiment in order to solve that problem by doping-Sb.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.7
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• pp.629-637
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• 2008

We report several experimental data capable of evaluating the amorphous-to-crystalline (a-c) phase transformation in $(Ag)_x(Ge_2Sb_2Te_5)_{1-x}$ (x = 0, 0.05, 0.1) thin films prepared by a thermal evaporation. The isothermal a-c structural phase changes were evaluated by XRD, and the optical transmittance was measured in the wavelength range of $800{\sim}3000$ nm using a UV-vis-IR spectrophotometer. A speed of the a-c transition was evaluated by detecting the reflection response signals using a nano-pulse scanner with 658 nm laser diode (power P = $1{\sim}17$ mW, pulse duration t = $10{\sim}460$ ns). The surface morphology and roughness of the films were imaged by AFM. It was found that the crystallization speed was so enhanced with an increase of Ag content. While the sheet resistance of c-phase $(Ag)_x(Ge_2Sb_2Te_5)_{1-x}$ was similar to that of c-phase $Ge_2Sb_2Te_5$ (i.e., $R_c{\sim}10{\Omega}/{\square}$), the sheet resistance of a-phase $(Ag)_x(Ge_2Sb_2Te_5)_{1-x}$ was found to be lager than that of a-phase $Ge_2Sb_2Te_5$, $R_a{\sim}5{\times}10^6{\Omega}{/\square}$. For example, the ratios of $R_a/R_c$ for $Ge_2Sb_2Te_5$ and $(Ag)_{0.1}(Ge_2Sb_2Te_5)_{0.9}$ were approximately $5{\times}10^5$ and $5{\times}10^6$, respectively.

• 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.