• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.05a
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• pp.110-110
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• 2009

최근 차세대 비휘발성 메모리(NVM) 기술은 메모리의 성능과 기존의 한계점을 효과적으로 극복하며 활발한 연구를 통해 비약적으로 발전하고 있으며 특히, phase-change random access memory (PRAM)은 ferroelectric random access memory (FeRAM)과 magneto-resistive random access memory (MRAM)과 같은 다른 NVM 소자와 비교하여 기존의 DRAM과 구조적으로 비슷하고 상용화가 빠르게 진행될 수 있을 것으로 예상되는 바, PRAM에 사용되는 상변화 물질의 식각을 수행하고 X-ray photoelectron spectroscopy (XPS)를 통해 표면의 열화현상을 관찰하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.74.1-74.1
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• 2007

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.1
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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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• 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 KIEE Conference
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• 2007.07a
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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.

• International Journal of Internet, Broadcasting and Communication
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• v.10 no.4
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• pp.6-11
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• 2018

As embedded memory technology evolves, the traditional Static Random Access Memory (SRAM) technology has reached the end of development. For deepening the manufacturing process technology, the next generation memory technology is highly required because of the exponentially increasing leakage current of SRAM. Non-volatile memories such as STT-MRAM (Spin Torque Transfer Magnetic Random Access Memory), PCM (Phase Change Memory) are good candidates for replacing SRAM technology in embedded memory systems. They have many advanced characteristics in the perspective of power consumption, leakage power, size (density) and latency. Nonetheless, nonvolatile memories have two major problems that hinder their use it the next-generation memory. First, the lifetime of the nonvolatile memory cell is limited by the number of write operations. Next, the write operation consumes more latency and power than the same size of the read operation.These disadvantages can be solved using the compiler. The disadvantage of non-volatile memory is in write operations. Therefore, when the compiler decides the layout of the data, it is solved by optimizing the write operation to allocate a lot of data to the SRAM. This study provides insights into how these compiler and architectural designs can be developed.

• IEIE Transactions on Smart Processing and Computing
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• v.5 no.5
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• pp.337-345
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• 2016

Recently, as the number of cores in computer systems has increased, the need for larger memory capacity has also increased. Unfortunately, dynamic random access memory (DRAM), popularly used as main memory for decades, now faces a scalability limitation. Phase change memory (PCM) is considered one of the strong alternatives to DRAM due to its advantages, such as high scalability, non-volatility, low idle power, and so on. However, since PCM suffers from short write endurance, direct use of PCM in main memory incurs a significant problem due to its short lifetime. To solve the lifetime limitation, many studies have focused on reducing the number of bit flips per write request. In this paper, we describe the PCM operating principles in detail and explore various bit flip reduction schemes. Also, we compare their performance in terms of bit reduction rate and lifetime improvement.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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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 the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.5
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• pp.329-333
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• 2012

For phase transition method, good record sensitivity, low heat radiation, fast crystallization and hi-resolution are essential. Also, a retention time is very important part for phase-transition. In our past papers, we chose composition of $Ge_1Se_1Te_2$ material to use a Se factor which has good optical sensitivity than conventional Sb. Sb/Ge-Se-Te thin films are fabricated and irradiated with UV light source to investigate a reversible phase change by Sb-doped condition. Because of Sb atoms, the Sb inserted sample showed better performance than conventional one. We should note that this novel one showed another possibility for phase-change random access memory.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.3
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• pp.146-152
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• 2011

Thermal stability of $Ge_2Sb_2Te_5$ (GST) and $SiO_2$ doped GST (SGST) films for phase change random access memory applications was investigated by observing the change of surface roughness, layer density and composition of both films after isothermal annealing. After both GST and SGST films were annealed at $325^{\circ}C$ for 20 min, root mean square (RMS) surface roughness of GST was increased from 1.9 to 35.9 nm but that of SGST was almost unchanged. Layer density of GST also steeply decreased from 72.48 to 68.98 $g/cm^2$ and composition was largely varied from Ge : Sb : Te = 22.3 : 22.1 : 55.6 to 24.2 : 22.7 : 53.1, while those of SGST were almost unchanged. It was confirmed that the addition of a small amount of $SiO_2$ into GST film restricted the deterioration of physical and chemical properties of GST film, resulting in the better thermal stability after isothermal annealing.