• 대한전자공학회논문지SD
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• 제44권1호
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• pp.45-50
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• 2007

본 논문에서는 상변환 메모리 (phase-change random access memory: PRAM)의 저전력 선택적 데이터 쓰기(selective data write: SDW) 기법을 제안하였다. PRAM은 쓰기 동작 과정에서 큰 전류를 오랜 시간동안 소모하기 때문에 큰 쓰기 전력을 소모한다. 이 쓰기 전력을 줄이기 위하여, SDW 기법은 쓰기 동작 과정에서 PRAM 셀에 데이터를 쓰기 전에 우선 저장될 셀의 데이터를 읽어온다. 셀의 기존 데이터와 새롭게 저장할 데이터를 비교하여, 입력된 데이터와 저장된 데이터가 다른 경우에만 PRAM 셀에 데이터 쓰기를 수행한다. 제안된 쓰기 기법을 사용하여 전력 소모를 반 이상으로 줄일 수 있다. 1Kbits ($128{\times}8bits$) PRAM 테스트 칩을 $0.5{\mu}m$ GST 셀과 $0.8{\mu}m$ CMOS 공정을 사용하여 구현하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권1호
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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 $705^{\circ}C$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1335-1336
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• 2007

Among the emerging non-volatile memory technologies, phase change memories are the most attractive in terms of both performance and scalability perspectives. Phase-change random access memory(PRAM), compare with flash memory technologies, has advantages of high density, low cost, low consumption energy and fast response speed. However, PRAM device has disadvantages of set operation speed and reset operation power consumption. In this paper, we investigated scalability of $Ge_{1}Se_{1}Te_{2}$ chalcogenide material to improve its properties. As a result, reduction of phase change region have improved electrical properties of PRAM device.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.205-206
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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 bottom electrode were investigated for PRAM. The 100-nm thick GST films were deposited on TiN/Si and TiAlN/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).

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.162-168
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• 2008

In this paper, we analyzed the heat transfer phenomenon and the reset current variation of PRAM device with thickness of phase change material using the 3-D finite element analysis tool. From the simulation, Joule's heat was generated at the contact surface of phase change material and bottom electrode of PRAM. As the thickness of phase change material was decreased, the reset current was highly increased. In case thickness of phase change material thin film was $200\;{\AA}$, heat increased through top electrode and reset current caused by phase transition highly increased. And as thermal conductivity of top electrode decreased, temperature of unit memory cell was increased.

• Journal of Advanced Marine Engineering and Technology
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• 제29권6호
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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 $125^{\circ}C$.

• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.410-416
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• 2007

PRAM (Phase change random access memory) is one of the most promising candidates for next generation non-volatile memories. However, the high reset current is one major obstacle to develop a high density PRAM. One way of the reset current reduction is to change the heater electrode material. In this paper, to reduce the reset current for phase transition, we have investigated the effect of heater electrode material parameters using finite element analysis. From the simulation. the reset current of PRAM cell is reduced from 2.0 mA to 0.72 mA as the electrical conductivity of heater is decreased from $1.0{\times}10^6\;(1/{\Omega}{\cdot}m$) to $1.0{\times}10^4\;(1/{\Omega}{\cdot}m$). As the thermal conductivity of heater is decreased, the reset current is slightly reduced. But the reset current of PRAM cell is not changed as the specific heat of heater is changed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.282-282
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• 2011

Low power consuming operation of phase-change random access memory (PRAM) can be achieved by confining the switching volume of phase change media into nanometer scale. Ge2Sb2Te5 (GST) is one of the best materials for the phase change random access memory (PRAM) because the GST has two stable states, namely, high and low resistance values, which correspond to the amorphous and crystalline phases of GST, respectively. However, achieving the fast operation speed at lower current requires an alternative chalcogenide material to replace the GST and shrinking the dimension of programmable volume. In this paper, we have fabricated nanoscale contact area on Ge2Sb2Te5 thin films with trimming process. The GST material was fabricated by melt quenching method and the GST thin films were deposited with thickness of 100 nm by the electron beam evaporation system. As a result, the reset current can be safely scaled down by reducing the device contact area and we could confirmed the phase-change characteristics by applying voltage pulses.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.154-155
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• 2007

PRAM(Phase-Change RAM) is a promising memory that can solve the problem of conventional memory and has the nearly ideal memory characteristics. We reviewed the issues for high density PRAM integration. Writing current reduction is the most urgent problem for high density PRAM realization. So, we studied new constitution of $Ge_1Se_1Te_2$ chalcogenide material and presented the method of reducing the contact size between $Ge_1Se_1Te_2$ and electrode. A small-contact-area electrode is used primarily to supply current into and minimize heat loss from the chalcogenide. In this letter, we expect the method of reducing the contact size between $Ge_1Se_1Te_2$ and electrode to decrease writing current.

• 정보과학회 논문지
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• 제42권3호
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• pp.379-389
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• 2015

Phase Change Memory (PCM 또는 PRAM), Magneto Resistive RAM (MRAM)과 같은 차세대 비휘발성 메모리가 등장하면서, Dynamic Random-Access Memory (DRAM)을 PRAM으로 대체하는 연구가 활발히 진행되고 있다. 본 논문에서는 PRAM을 메인 메모리로 사용하는 시스템에서 지금까지 널리 사용되고 있는 기존의 조인 알고리즘(블록 네스티드 조인, 소트-머지 조인, 그레이스 해시 조인, 하이브리드 해시 조인)들을 사용했을 때 발생하는 내구성과 성능 문제를 비교, 분석한다. 본 연구의 실험결과에 의하면 기존의 조인 알고리즘들을 PRAM에 맞게 재설계해야 하는 필요성이 제기되었다. 특히, 본 연구는 조인 알고리즘들을 PRAM에 적용했을 때 발생하는 이슈들을 과학적으로 규명한 첫 시도이다. 그리고 기존의 조인 알고리즘들을 PRAM에 적용했을 때 발생하는 내구성과 성능을 비교하기 위한 PRAM 기반의 시스템을 모델링하고 시뮬레이터를 구현한 것에 연구의 의의를 둘 수 있다.