• Proceedings of the Optical Society of Korea Conference
• /
• 2007.02a
• /
• pp.175-176
• /
• 2007

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.48 no.5
• /
• pp.74-82
• /
• 2011

SSD has a limitation of number of erase/write cycles and does not allow in-place update unlike the hard disk because SSD is composed of an array of NAND flash memory. Thus, FTL is used to effectively manage SSD of having different characteristics from traditional disk. FTL has page, block, log-block mapping method. Among then, when log-block mapping method such as BAST and FAST is used, the performance of SSD is degraded because frequent merge operations cause lots of pages to be copied and deleted. This paper proposes a data allocation and replacement method based on access frequency by allocating PRAM as checking area of access frequency, log blocks, storing region of hot data in SSD. The proposed method can enhance the performance and lifetime of SSD by storing cold data to flash memory and storing log blocks and frequently accessed data to PRAM and then reducing merge and erase operations. Besides, a data replacement method is used to increase utilization of PRAM which has limitation of capacity. The experimental results show that the ratio of erase operations of the proposed method is 46%, 38% smaller than those of BAST and FAST and the write performance of the proposed method is 34%, 19% higher than those of BAST and FAST, and the read performance of the proposed method is 5%, 3% higher than those of BAST and FAST, respectively.

• Journal of Advanced Marine Engineering and Technology
• /
• v.29 no.6
• /
• pp.707-712
• /
• 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 Vacuum Society Conference
• /
• 2011.08a
• /
• pp.282-282
• /
• 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.

• Journal of Advanced Marine Engineering and Technology
• /
• v.31 no.4
• /
• pp.410-416
• /
• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.06a
• /
• pp.154-155
• /
• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.07a
• /
• pp.203-204
• /
• 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).

• Journal of the Korean Ceramic Society
• /
• v.44 no.1 s.296
• /
• pp.18-22
• /
• 2007

The phase transition behavior of $Ge_2Sb_2Te_5$ (GST) thin film, which is a candidate material of recording layer for phase change random access memory (PRAM), has been evaluated using an in-situ reflectance measurement method. The experimental data have been analyzed by using johnson-mehl-avrami-kolomogorov (JMAK) model. JMAK model can be used only in isothermal state. However, temperature changes with time during the operation of PRAM. To apply JMAK equation to PRAM simulation, it has been assumed that the temperature increases stepwise and isothermally. By using JMAK equation and assumption for the transient state, the phase transition behavior of GST thin film has been predicted under $3^{\circ}C/min$ heating rate in this study. The simulation result agrees well with the experimental results. Therefore, It can be concluded that JMAK equation can be used far the PRAM simulation model.

• ETRI Journal
• /
• v.21 no.2
• /
• pp.22-30
• /
• 1999

In this paper, we derive an efficient parallel algorithm to solve the single function coarsest partition problem. This algorithm runs in O(\log2n) time using O(nlogn) operations on the EREW PRAM with O(n) memory cells used. Compared with the previous PRAM algorithms that consume O(n1+${\varepsilon}$) memory cells for some positive constant ${\varepsilon}\>0$, our algorithm consumes less memory cells without increasing the total number of operations.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.17 no.3
• /
• pp.363-369
• /
• 2017

Phase-change random access memory (PRAM) has been emerged as a potential memory due to its excellent scalability, non-volatility, and random accessibility. But, as the cell current is reducing due to cell size scaling, the read-sensing window margin is also decreasing due to increased variation of cell performance distribution, resulting in a substantial loss of yield. To cope with this problem, a novel adaptive read-sensing reference current generation scheme is proposed, whose trimming range and resolution are adaptively controlled depending on process conditions. Performance evaluation in a 58-nm CMOS process indicated that the proposed read-sensing reference current scheme allowed the integral nonlinearity (INL) to be improved from 10.3 LSB to 2.14 LSB (79% reduction), and the differential nonlinearity (DNL) from 2.29 LSB to 0.94 LSB (59% reduction).