• Journal of the Korean Ceramic Society
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• v.45 no.5
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• pp.276-279
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• 2008

In this research, properties of $N_2$-doped $Sb_2Te_3$ thin film were evaluated using 4-point probe, XRD and AFM. $Sb_2Te_3$ material has faster crystallization rate than $Ge_2Sb_2Te_5$, but sheet resistance difference between amorphous and crystallization state is very low. This low sheet resistance difference decreases sensing margin in reading operation at PRAM device operation. Therefore, in order to overcome this weak point, $N_2$ gas was doped on $Sb_2Te_3$ thin film. Sheet resistance difference between amorphous and crystallized state of $N_2$-doped $Sb_2Te_3$ thin film showed about $10^4$ times higher than Un-doped $Sb_2Te_3$ thin film because of the grain boundary scattering.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.6
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• pp.707-712
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• 2005

PRAM (Phase change random access memory) is one of the most promising candidates for next generation Non-volatile Memories. The Phase change materials have been researched in the field of optical data storage media. Among the phase change materials. $Ge_2Sb_2Te_5$ is very well known for its high optical contrast in the state of amorphous and crystalline. However the characteristics required in solid state memory are quite different from optical ones. In this study. the structural Properties of GeSbTe thin films with composition were investigated for PRAM. The 100-nm thick $Ge_2Sb_2Te_5$ and $Sb_2Te_3$ films were deposited on $SiO_2/Si$ substrates by RF sputtering system. In order to characterize the crystal structure and morphology of these films. x-ray diffraction (XRD). atomic force microscopy (AFM), differential scanning calorimetry (DSC) and 4-point measurement analysis were performed. XRD and DSC analysis result of GST thin films indicated that the crystallization of $Se_2Sb_2Te_5$ films start at about $180^{\circ}C$ and $Sb_2Te_3$ films Start at about $125^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.52-52
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• 2009

To date, chalcogenide alloy such as $Ge_2Sb_2Te_5$(GST) have not only been rigorously studied for use in Phase Change Random Access Memory(PRAM) applications, but also temperature gap to make different states is not enough to apply to device between amorphous and crystalline state. In this study, we have investigated a new system of phase change media based on the In-Sb-Te(IST) ternary alloys for PRAM. IST chalcogenide thin films were prepared in trench structure (aspect ratio 5:1 of length=500nm, width=100nm) using Tri methyl Indium $(In(CH_3)_4$), $Sb(iPr)_3$ $(Sb(C_3H_7)_3)$ and $Te(iPr)_2(Te(C_3H_7)_2)$ precursors. MOCVD process is very powerful system to deposit in ultra integrated device like 100nm scaled trench structure. And IST materials for PRAM can be grown at low deposition temperature below $200^{\circ}C$ in comparison with GST materials. Although Melting temperature of 1ST materials was $\sim 630^{\circ}C$ like GST, Crystalline temperature of them was ~$290^{\circ}C$; one of GST were $130^{\circ}C$. In-Sb-Te materials will be good candidate materials for PRAM applications. And MOCVD system is powerful for applying ultra scale integration cell.

• 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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• 2005.07a
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• pp.203-204
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• 2005

PRAM (Phase change Random Access Memory) is one of the most promising candidates for next generation Non-volatile Memories. The Phase change material has been researched in the field of optical data storage media. Among the phase change materials $Ge_2Sb_2Te_5$(GST) is very well known for its high optical contrast in the state of amorphous and crystalline. However, the characteristics required in solid state memory are quite different from optical ones. In this study, the structural properties of GST thin films with composition were investigated for PRAM. The 100-nm thick GeTe and $Sb_2Te_3$ films were deposited on $SiO_2$/Si substrates by RF sputtering system. In order to characterize the crystal structure and morphology of these films, we performed x-ray diffraction (XRD) and atomic force microscopy (AFM).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.132-133
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• 2006

PRAM (phase-change random access memory)은 전류 펄스 인가에 따른 기록매질의 비정질-결정질 간 상변화와 그에 동반되는 저항변화를 이용하는 차세대 비휘발성 메모리 소자로서 연구되어지고 있다. 본 논문에서는 $(GeTe)_x(Sb_2Te_3)$ pseudobinary line을 따르는 조성(x=0.5, 1, 2, 8)의 벌크 및 박막시료를 제작하고 원자-스케일의 구조적 상변화를 분석하였다. 열증착을 이용하여 Si 기판위에 200nm 두께의 박막을 형성, 질소분위기 하에서 100-450도 범위에서 열처리 하였다. XRD를 통해 열처리 온도에 따른 구조적 분석을 실시하였다. x=8의 조성을 제외한 전체 박막에 대해 열처리 온도 증가에 따라 fcc와 hexagonal 구조가 순차적으로 나타났으며 일부에서는 혼종의 상구조를 보였다. 특히, $Ge_2Sb_2Te_5$ 박막에 대하여 EXAFS (extended x-ray absorption fine structure) 및 XPS를 이용하여 상변화의 원자-스케일 구조분석을 하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.3
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• pp.199-205
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• 2010

The crystallization speed (v) of amorphous (InTe)$_x$(GeTe) (x = 0.1, 0.3 and 0.5) films and their thermal, optical and electrical behaviors have been investigated using nano-pulse scanner (wavelength = 658 nm, laser beam diameter < 2 ${\mu}m$), X-ray diffraction (XRD), 4-point probe and UV-vis-IR spectrophotometer. These results were compared with those of $Ge_2Sb_2Te_5$ (GST) film, comprehensively utilized for phase-change random access memory (PRAM). Both v-value and thermal stability of (InTe)$_{0.1}$(GeTe) and (InTe)$_{0.3}$(GeTe) films could be enhanced in comparison with those of the GST. Contrarily, the v-value in the (InTe)$_{0.5}$(GeTe) film was so drastically deteriorated that we could not quantitatively evaluate it. This deterioration is thought because amorphous (InTe)$_{0.5}$(GeTe) film has relatively high reflectance, resulting in too low absorption to cause the crystallization. Conclusively, it could be thought that a proper compositional (InTe)$_x$(GeTe) films (e.g., x < 0.3) may be good candidates with both high crystallization speed and thermal stability for PRAM application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.7
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• pp.585-593
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• 2008

In this work, we report several experimental data capable of evaluating the phase transformation characteristics of GeSbTe pseudobinary thin films comprehensively utilized as phase change materials. The phase transformation of the GeSbTe thin films was confirmed by XRD measurement from amorphous to hexagonal structure via fee structure except for $Ge_8Sb_2Te_{11}$. In addition, X-ray photoelectron spectra analysis revealed to weaken Ge-Te bond for $Ge_2Sb_2Te_5$ and to strengthen the bonds of all elements for $Ge_8Sb_2Te_{11}$ during the amorphous to crystalline transition. The values of optical energy gap $(E_{OP})$ were around 0.71 and 0.50 eV and the slopes of absorption in extended region (B) were ${\sim}5.1{\times}10^5$ and ${\sim}10{\times}10^5cm^{-1}{\cdot}V^{-1}$ for the amorphous and fcc-crystalline structures, respectively. Finally, the kinetics of amorphous-to-crystalline phase change on the GeSbTe films was characterized using a nano-pulse scanner with 658-nm laser diode (power; $1{\sim}17$ mW, pulse duration; $10{\sim}460$ ns).

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.131-137
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• 2009

In this paper, we have manufactured hole type PRAM unit cell using phase change material $Ge_2Sb_2Te_5$. The phase change material $Ge_2Sb_2Te_5$ was deposited on hole of 500 nm size using sputtering method. Reset current of PRAM unit cell was confirmed by measuring R-V characteristic curve. Reset current of manufactured hole type PRAM unit cell is 15 mA, 100 ns. And electro and thermal characteristics of hole type PRAM unit cell were analyzed by 3-D finite element analysis. From simulation temperature of PRAM unit cell was $705^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.186-186
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• 2013

Nitrogen doped Ge-Sb-Te (N-GST) thin films for phase change random access memory (PRAM) applications were investigated by synchrotron-radiation-based x-ray photoelectron spectroscopy and absorption spectroscopy. Nitrogen doping in GST resulted in more favorable N atoms' bonding with Ge atoms rather than with Sb and Te atoms [1,2], which explains the higher phase change transition temperature than that of undoped Ge-Sb-Te thin film. Surprisingly, it was noticed that N atoms also existed in the form of molecular nitrogen, $N_2$, which is detrimental to the stability of the GST performance [3]. N-doped GST experimental features were also supported by ab-initio molecular dynamic calculations [2]. References [1] M.-C. Jung, Y. M. Lee, H.-D. Kim, M. G. Kim, and H. J. Shin, K. H. Kim, S. A. Song, H. S. Jeong, C. H. Ko, and M. Han, "Ge nitride formation in N-doped amorphous Ge2Sb2Te5", Appl. Phys. Lett. 91, 083514 (2007). [2] Zhimei Sun, Jian Zhou, Hyun-Joon Shin, Andreas Blomqvist, and Rajeev Ahuja, "Stable nitride complex and molecular nitrogen in N doped amorphous Ge2Sb2Te5", Appl. Phys. Lett. 93, 241908 (2008). [3] Kihong Kim, Ju-Chul Park, Jae-Gwan Chung, and Se Ahn Song, Min-Cherl Jung, Young Mi Lee, Hyun-Joon Shin, Bongjin Kuh, Yongho Ha, Jin-Seo Noh, "Observation of molecular nitrogen in N-doped Ge2Sb2Te5", Appl. Phys. Lett. 89, 243520 (2006).