• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.715-719
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• 2009

The phase change electrode board for the bio-information detection through electrical property response of phase change material was developed in this study. We manufactured the electrode board using Aluminum first that is widely used in conventional semiconductor device process. Without further treatment, these aluminum electrodes tend to contain voids in PETEOS(plasma enhanced tetraethyoxysilane) material that are easily detected by cross-sectional SEM(Scanning Electron Microscope). The voids can be easily attacked and transformed into holes in between PETEOS and electrodes after etch back and washing process. In order to resolve this issue of Al electrode board, we developed a electrode board manufacturing method using low resistivity TiN, which has advantages in terms of the step-coverage of phase change($Ge_2Sb_2Te_5$, GST) thin film as well as thermodynamic stability, without etch back and washing process. This TiN material serves as the top and bottom electrode in PRAM(Phase-change Random Access Memory). The good connection between the TiN electrode and GST thin film was confirmed by observing the cross-section of TiN electrode board using SEM. The resistances of amorphous and crystalline GST thin film on TiN electrodes were also measured, and 1000 times difference between the amorphous and crystalline resistance of GST thin film was obtained, which is well enough for the signal detection.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.21-22
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• 2008

In the paper, we report several experimental data capable of evaluating the phase transformation characteristics of $Ag_x(Ge_2Sb_2Te_5)_{1-x}$ (x =0, 0.05, 0.1) thin films. The $Ag_x(Ge_2Sb_2Te_5)_{1-x}$ phase change thin films have been prepared by thermal evaporation. The crystallization characteristics of amorphous$Ag_x(Ge_2Sb_2Te_5)_{1-x}$ thin films were investigated by using nano-pulse scanner with 658 nm laser diode (power; 1~17 mW, pulse duration; 10~460 ns) and XRD measurement. It was found that the more Ag is doped, the more crystallization speed was 50 improved. In comparision with $Ge_2Sb_2Te_5$ thin film, the sheet resistance$(R_{amor})$ of the amorphous $Ag_x(Ge_2Sb_2Te_5)_{1-x}$ thin films were found to be lager than that of $Ge_2Sb_2Te_5$ film($R_{amor}$ $\sim10^7\Omega/\square$ and $R_{cryst}$ 10 $\Omega/\square$). That is, the ratio of $R_{amor}/R_{cryst}$ was evaluates to be $\sim10^6$ This is very helpful to writing current reduction of phase-change random acess memory.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.1
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• pp.32-39
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• 2011

The purpose of VDR capsule is to maintain a stored information securely and retrievably in the extreme environment like voyage incident. This study shows the modellings, the analyses and the experiments of the survivability test of penetration, high and low temperature fire. The capsule housing is used to protect capsule against penetration and the influences of its thickness are studied by the modelling and analysis of penetration using LS-DYNA. The phase change material and thermal insulation material are used to protect capsule against high and low temperature fire test. The thermal characteristics of various volume ratios of phase change material to thermal insulation material were conducted. Also the tests were conducted to confirm the structural and thermal reliability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.67-68
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• 2009

In this study, we studied the nature of thin films formed by photodoping chalcogenide materials with for use in programmable metallization cell devices, a type of ReRAM. We investigated the resistance of Ag-doped chalcogenide thin films varied in the applied voltage bias direction from about $1\;M{\Omega}$ to several hundreds of $\Omega$. As a result of these resistance change effects, it was found that these effects agreed with PMC-RAM. The results imply that a Ag-rich phase separates owing to the reaction of Ag with free atoms from the chalcogenide materials.

• Transactions of the Society of Information Storage Systems
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• v.1 no.2
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• pp.132-136
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• 2005

It is widely accepted that the reading mechanism of Super-RENS(super-resolution near field structure) and Super-ROM(super-resolution read only memory) is closely related with non-linear temperature dependent material properties such as refractive indices, phase change. Furthermore, the dynamic change of the temperature distribution also an essential part of reading mechanism of Super-RENS/ROM. Therefore, the knowledge of the temperature distribution as a function a time is one of the important keys to reveal the physics of reading mechanism in Super-RENS/ROM. We calculated time-dependent temperature distribution in a 3-dimensional Super-ROM disk structure when moving laser beam is irradiated. With a help of commercial software FEMLAB which employed finite element method, we simulated the temperature distribution of ROM structure whose pit diameter is 120-nm with 50-nm depth. Energy absorption by moving laser irradiation, time variations of heat transfer processes, heat fluxes, heat transfer ratios, and temperature distributions of the complicate 3-dimensional ROM structure have been obtained.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.23-23
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• 2009

Recently, the nanowire configuration of GST showed nanosecond-level phase switch at very low power dissipation, suggesting that the nanowires could be ideal for data storage devices. In spite of many advantages of IST materials, their feasibility in both thin films and nanowires for electronic memories has not been extensively investigated. The synthesis of the chalcogenide nanowires was mainly preformed via a vapor transport process such as vapor-liquid-solid (VLS) growth at a high temperature. However, in this study, IST nanowires as well as thin films were prepared at a low temperature (${\sim}250^{\circ}C$) by metal organic chemical vapor deposition(MOCVD) method, which is possible for large area deposition. The IST films and/or nanowires were selectively grown by a control of working pressure at a constant growth temperature by MOCVD. In-Sb-Te NWs will be good candidate materials for high density 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.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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.70-70
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• 2009

Si 도핑한 $Ge_2Sb_2Te_5$ 박막은 비정질상에서의 열적 안정성증가, fcc에서 hex상으로의 상전이 억제, 활성화 에너지 증가 등의 특성을 보인다. 본 연구에서는 Si 도핑에 의한 $Ge_2Sb_2Te_5$ 박막의 전기적 그리고 구조적인 특성에 관한 실험을 진행하였다. 실험에 사용된 Si 도핑 $Ge_2Sb_2Te_5$ 박막은 Si 기판 위에 radio frequency power supply를 사용해 Si과 $Ge_2Sb_2Te_5$ 타겟을 co-sputtering하여 증착하였다. Si의 sputtering 파워를 달리하여 실리콘의 농도를 다르게 증착 하였고 X-ray photoelectron spectroscopy (XPS)를 사용하여 박막의 Si 농도를 측정하였다. 증착된 박막은 질소 분위기 하에서 $5\;^{\circ}C$/min으로 열처리 하여 여러 온도와 Si 농도에서의 박막의 특성을 측정하였다. 열처리 전, 후의 박막은 X-ray diffraction (XRD) 분석을 통하여 각각의 온도에서의 구조적 특성을 분석하였다. 열처리 온도에 따르는 필름의 전기적 특성 파악을 위해서 four-point probe를 이용하여 박막의 면저항을 측정하였고 그 값은 3 회 이상 측정하여 평균값을 사용하였다. Nano-pulse scanner를 사용하여 다양한 파워범위와 펄스폭 범위에서의 박막의 상변화에 따른 반사도 차이를 측정하여 각 조성에서의 비정질-결정질상 변화속도를 분석하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.203-206
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• 2004

For the realization of PRAM, $Ge_2Sb_2Te_5$ (GST) has been employed for the phase transition between the crystal and amorphous states by electrical joule heating. Although there has been a vast amount of results concerning the GST in material aspect for the laser-induced optical storage disc applications, the process-related issues of GST for the PRAM applications have not been reported. In this work, the etching behaviors of GST were investigated when the processing conditions were varied in the high-density helicon plasma. The etching parameters of RF main power, RF bias power, and chamber pressure were fixed at 600 W, 150 W, and 5 mTorr, respectively. For the etching processes, gas mixtures of $Ar/Cl_2$, $Ar/CF_4$, and $Ar/CHF_3$ were employed, in which the etching rates and etching selectivities of GST thin film in given gas mixtures were evaluated. From obtained results, it is found that we can arbitrarily design the etching process according to given cell structures and material combinations for PRAM cell fabrications.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.55-55
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• 2010

상변화 메모리용 셀은 전류 구동형으로써 셀에 전류를 인가하였을 때 저항이 높은 상태(비정질상)과 저항이 낮은 상태(결정질상)의 두가지 특성을 갖는다. 저항이 높은 상태에서 전류나 전압을 인가하면 높은 저항을 보이다가 일정 값(threshold voltage) 이상에서 낮은 저항을 갖는 현상을 보인다. 이때 상변화물질의 종류 혹은 셀의 사이즈에 따라 threshold voltage의 차이가 나타나는데 이 값을 줄임으로서 상변화 메모리의 구동 전류의 감소에 기여할 수 있다. 본 연구에서는 스퍼터링 방법을 이용해 박막형식의 셀을 제작하여 전기적 특성을 관찰하였다. 셀은 Si 기판 위에 radio frequency power supply 와 direct current power supply를 사용해 하부전극과 상변화층, 그리고 상부전극의 순으로 증착하여 제작하였다. 상변화층은 $Ge_2Sb_2Te_5$를 사용하였고 제작된 셀은 scanning electon microscope(SEM)를 이용하여 표면의 상태를 확인하였고 Keithley 4200scs를 이용하여 인가된 전류 혹은 전압에 따른 특성변화를 측정하였다.