• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 추계총회 및 연구발표회 초록집
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• pp.192.2-192
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• 2003

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권6호
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• pp.297-301
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• 2006

In the present work, we investigate the characteristics of new composition material, chalcogenide $Ge_1Se_1Te_2$ material in order to overcome the problems of conventional PRAM devices. The Tc of $Ge_1Se_1Te_2$ bulk was measured $231.503^{\circ}C$ with DSC analysis. For static DC test mode, at low voltage, two different resistances are observed. depending on the crystalline state of the phase-change resistor. In the first sweep, the as-deposited amorphous $Ge_1Se_1Te_2$ showed very high resistance. However when it reached the threshold voltage(about 11.8 V), the electrical resistance of device was drastically reduced through the formation of an electrically conducting path. The phase transition between the low conductive amorphous state and the high conductive crystal]me state was caused by the set and reset pulses respectively which fed through electrical signal. Set pulse has 4.3 V. 200 ns. then sample resistance is $80\sim100{\Omega}$. Reset pulse has 8.6 V 80 ns, then the sample resistance is $50{\sim}100K{\Omega}$. For such high resistance ratio of $R_{reset}/R_{set}$, we can expect high sensing margin reading the recorded data. We have confirmed that phase change properties of $Ge_1Se_1Te_2$ materials are closely related with the structure through the experiment of self-heating layers.

• 한국전기전자재료학회논문지
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• 제11권4호
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• pp.314-320
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• 1998

In this study, we have investigated crystallization properties of $Te_x(Sb_{85}Ge_{15})_{100-x}$ (x=0.3, 0.5, 1.0) thin films prepared by thermal evaporation. The change of reflectance according to phase change from amorphous to crystalline phases with annealing and exposure of diode laser is measured b the n&k analyzer and the surface morphology between amorphous and crystalline phase is analyzed by SEM and AFM. The difference in reflectance($\DeltaR$) between amorphous and crystalline phase appears approximately 20% at the diode laser wavelength, 780nm in all prepared films. Especially, the reflectance difference,$\DeltaR$ comes up to about 30% in $Te_{0.5}(Sb_{85}Ge_{15})_{99.5}$ thin film. Also, amorphous-to-crystalline phase change is observed in all prepared films. As a result of the measurement of the reflectance using diode laser, the reflectance is increased in proportion to the laser power and exposure time in all films. As a result of observing each film with the SEM and AFM, the surface morphology of the annealed and the exposed films are evidently increased than those of as-deposited films. The fast crystallization is occurred by increasing in Te content. Therefore, we conclude that the $Te_{0.5}(Sb_{85}Ge_{15})_{99.5}$ and $Te_1(Sb_{85}Ge_{15})_{99}$ thin films can be evaluated as an attractive optical recording medium with high contast ratio and fast erasing time due to crystallization.

• 정보저장시스템학회논문집
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• 제1권1호
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• pp.34-41
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• 2005

We report some recent results in the rewritable Blu-ray Disc with enhanced overwrite cyclability by using the growth dominant eutectic based Ge(Sb70Te30)+Sb recording layer, GeN interface layer and write strategy optimization. We have developed phase-change optical media with appropriate write strategy for 36(i.e., 1X)-72Mbps(i.e., 2X) dual speed Blu-ray Disc system and fur the future high speed optical data storage. For recording layer, eutectic-based Ge(Sb70Te30)+Sb material was used and Sb/Te ratio and Ge content were optimized to obtain proper erasability and archival stability of recorded amorphous marks. The recording layer is wrapped up in GeN interface layers to obtain overwrite cyclability and higher crystallization speed. In addition, we designed appropriate write strategy so called Time-Shifted Multipulse (TSMP) write strategy where starting position of multipulse parts are shined from reference clock. With this write strategy, the jitter characteristics of the disc was improved and we found that leading edge jitter was improved much more than trailing edge jitter in 1X-2X speed recording. Finally, we investigated the higher speed feasibility of 144Mbps(i.e., 4X) by adopting some elemental doping to the eutectic based Ag-In-Sb-Te recording layer and structural optimization of constitution layers in Blu-ray Disc. In the paper, we report the effect of Sn addition for the feasibility of higher speed recording. The addition of Sn shows increases of the crystallization speed of phase change recording layer.

• 한국분말재료학회지
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• 제18권5호
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• pp.449-455
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• 2011

In this study, p-type $(AgSbTe_2)_{15}(GeTe)_{85}$: TAGS-85 compound powders were prepared by gas atomization process, and then their microstructures and mechanical properties were investigated. The fabricated powders were of spherical shape, had clean surface, and illustrated fine microstructure and homogeneous $AgSbTe_2$ + GeTe solid solution. Powder X-ray diffraction results revealed that the crystal structure of the TAGS-85 sample was single rhombohedral GeTe phase, which with a space group $R_{3m}$. The grain size of the powder particles increased while the micro Vickers hardness decreased with increasing annealing temperature within the range of 573 K and 723 K due to grain growth and loss of Te. In addition, the crystal structure of the powder went through a phase transformation from rhombohedral ($R_{3m}$) at low-temperature to cubic ($F_{m-3m}$) at high-temperature with increasing annealing temperature. The micro Vickers hardness of the as-atomized powder was around 165 Hv, while it decreased gradually to 130 Hv after annealing at 673K, which is still higher than most other fabrication processes.

• 한국전기전자재료학회논문지
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• 제32권6호
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• pp.448-453
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• 2019

This work reports the electrical characteristics of and temperature distribution in chalcogenide phase change memory (PCM) devices that have a self-aligned structure. GST (Ge-Sb-Te) chalcogenide alloy films were formed in a self-aligned manner by interdiffusion between sputter-deposited Ge and $Sb_2Te_3$ films during thermal annealing. A transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) analysis demonstrated that the local composition of the GST alloy differed significantly and that a $Ge_2Sb_2Te_5$ intermediate layer was formed near the $Ge/Sb_2Te_3$ interface. The programming current and threshold switching voltage of the PCM device were much smaller than those of a control device; this implies that a phase transition occurred only in the $Ge_2Sb_2Te_5$ intermediate layer and not in the entire thickness of the GST alloy. It was confirmed by computer simulation, that the localized phase transition and heat loss suppression of the GST alloy promoted a temperature rise in the PCM device.

• 한국광학회:학술대회논문집
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• 한국광학회 2003년도 제14회 정기총회 및 03년 동계학술발표회
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• pp.78-79
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• 2003

타원법(ellipsometry)을 사용하여 광기록 매체용 Ge$_2$Sb$_2$Te／sub 5／(GST) 박막의 성장과정에 따른 타원상수 Ψ와 $\Delta$를 측정하여, GST 박막의 최적성장조건을 연구하였다. 아르곤기체압력과 DC 출력 그리고 기판의 온도를 변화시키면서 GST 박막을 성장시켰다. 제작된 시료들의 분광타원 데이터를 모델링분석하여 GST 박막의 밀도분포를 구하고 한편으로는 GST 박막이 성장하는 동안 측정한 in situ 타원 성장곡선을 분석하여 박막의 밀도분포의 변화를 추적하였다. (중략)

• 한국전기전자재료학회논문지
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• 제23권4호
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• pp.261-266
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• 2010

In this paper, we report the changes of electrical, structural and optical characteristics in $Ge_2Sb_2Te_5$ thin films according to an increase of Si content. The Si-doped $Ge_2Sb_2Te_5$ thin films were prepared by rf-magnetron co-sputtering method. Isothermal annealing was carried out at $N_2$ atmosphere. The crystallization speed (v) of amorphous thin films was evaluated by detecting the reflection response signals using a nano-pulse scanner (wavelength = 658 nm) with illumination power of 1~17 mW and pulse duration of 10~460 ns. Structural phase changes were evaluated by XRD, and the optical transmittance was measured in the wavelength range of 300~3000 nm using UV-vis-NIR spectrophotometer. The sheet resistance (RS) of the thin films was measured using 4 point probe. Conclusivlely, the v-value decreased with an increase of Si content, while the RS-values of both crystalline and amorphous phases were increased. In particular, fcc-to-hexagonal transition was suppressed by the added Si atoms.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1329-1330
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• 2007

Phase-change random access memory(PRAM) has many advantages compare with the existing memory. For example, fast programming speed, low programming voltage, high sensing margin, low power consume and long cyclability of read/write. Though it has many advantages, there are some points which must be improved. So, we invented and studied new constitution of $Ge_{1}Se_{1}Te_{2}$ chalcogenide material. Actually, the performance properties have been improved surprisingly. However, crystallization time was as long as ever for amorphization time. In this paper, we studied in order to make set operation time and reset operation voltage reduced. In the present work, by alloying Sb in $Ge_{1}Se_{1}Te_{2}$. we could confirm that improved its set operation time and reset operation voltage. As a result, the method of Sb-alloyed $Ge_{1}Se_{1}Te_{2}$ can be solution to decrease the set operation time and reset operation voltage.

• 한국전기전자재료학회논문지
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• 제24권12호
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• pp.982-987
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• 2011

In this study, $Ge_8Se_{(2+x)}Te_{(6-x)}$ thin film amorphous-to-crystalline phase-change rate was evaluated in using a nano-pulse scanner. The focused laser beam with a diameter <10 ${\mu}m$ was illuminated in the power (P) and pulse duration (t) ranges of 1-31 mW and 10-460 ns, respectively, with subsequent detection of the responsive signals reflected from the film surface. We also evaluated the material characteristics, such as optical absorption and energy gap, crystalline phases, and sheet resistance of as-deposited and annealed films. The result of experiments showed that the thermal stability of the Ge-Se-Te film is largely improved by adding Se.