Pulse number control of electrical resistance for multi-level storage based on phase change

Nakayama, Keiichi I.; Takata, Masaki; Kasai, Tokuzo; Kitagawa, Akio; Akita, Junichi

doi:10.1088/0022-3727/40/17/009

Cited by 25 publications

(15 citation statements)

References 17 publications

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“…Recently, eight-level storage and three-bits in a single cell have been reported32. Currently, multi-level storage323334 has been realized by controlling the fraction of the crystalline33 or amorphous35 regions within one storage cell. However, realizing multi structures in GST could offer another way to achieve multi-level storage, for example, by creating and manipulating multi-levels in cubic GST with different degrees of vacancy ordering and resistivity3.…”

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confidence: 99%

Vacancy Structures and Melting Behavior in Rock-Salt GeSbTe

Zhang

Wang

Shen

et al. 2016

Sci Rep

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Ge-Sb-Te alloys have been widely used in optical/electrical memory storage. Because of the extremely fast crystalline-amorphous transition, they are also expected to play a vital role in next generation nonvolatile microelectronic memory devices. However, the distribution and structural properties of vacancies have been one of the key issues in determining the speed of melting (or amorphization), phase-stability, and heat-dissipation of rock-salt GeSbTe, which is crucial for its technological breakthrough in memory devices. Using spherical aberration-aberration corrected scanning transmission electron microscopy and atomic scale energy-dispersive X-ray mapping, we observe a new rock-salt structure with high-degree vacancy ordering (or layered-like ordering) at an elevated temperature, which is a result of phase transition from the rock-salt phase with randomly distributed vacancies. First-principles calculations reveal that the phase transition is an energetically favored process. Moreover, molecular dynamics studies suggest that the melting of the cubic rock-salt phases is initiated at the vacancies, which propagate to nearby regions. The observation of multi-rock-salt phases suggests another route for multi-level data storage using GeSbTe.

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confidence: 99%

Vacancy Structures and Melting Behavior in Rock-Salt GeSbTe

Zhang

Wang

Shen

et al. 2016

Sci Rep

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“…MLC PCM PROGRAMMING AND MODELING Resistance levels, which represent different states, are fundamentally determined by the relative amorphous fraction in PCM cells, which is in turn determined by the amount of energy delivered to the GST material during programming. As a result, to achieve different resistance levels, various number of reset/set iterations are needed to precisely deliver appropriate amount of energy [8], [13].…”

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confidence: 99%

Minimizing MLC PCM write energy for free through profiling-based state remapping

Zhao

Xue

Yang

2015

The 20th Asia and South Pacific Design Automation Conference

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Phase change memory is becoming one of the most promising candidates to replace DRAM as main memory in deep sub-micron regime. Multi-level cell (MLC) PCM outperforms single level cell (SLC) PCM in terms of storage capacity but requires an iterative programming-and-verifying scheme to program cells to different resistance levels. The energy consumed in programming different MLC states varies significantly, thus motivating a state remapping technique to minimize the overall write energy. In this paper, we first compare dynamic and static state remapping strategies in terms of their efficacy in reducing energy, and then propose an effective and low-cost static state remapping algorithm. The experimental studies show 10.6% average (up to 16.9%) reduction in MLC PCM write energy, achieved within negligible hardware and performance overhead. Compared with the most related work, the proposed scheme saves more write energy on average, with near-zero performance, area and energy overhead.

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“…[1] Increasing of memory storage density can be achieved using multilevel storage technology which has recently been attracting extensive attention for applications in nonvolatile memory devices. [2][3][4][5][6][7][8][9][10] In multilevel data storage, distinct multilevels states, instead of the common binary states, are utilized for the identification of storage levels. The number of different storage levels is determined by the maximum number of levels in a memory cell and is associated with the configuration of active materials state (amorphous, crystalline or mixture of both).…”

Section: Introductionmentioning

confidence: 99%

Realization of Multilevel States in Phase‐Change Thin Films by Fast Laser Pulse Irradiation

Sun

Lotnyk

Ehrhardt

et al. 2017

Advanced Optical Materials

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consumption. Routinely, the recording (amorphization) process is obtained by applying an intense and short pulse, either a laser or a current pulse, which induces melting and fast quenching, while a moderately intense and long laser/current pulse is used to thermally anneal the material above the crystallization temperature within a sufficient amount of time in the erasing (crystallization) process. With the application of multilevel storage, each appropriate excitation with a pulse contributes to achieving a partial crystallization/ amorphization and this allows multiple bits for recording/erasing of information in each memory cell, based on the respective mode of energy accumulation. [2,5,11] Consequently, the energy consumption per cell can be reduced.Phase-change material (PCM), like Ge-Sb-Te-based alloys, exhibit remarkable material properties: significantly fast crystallization and amorphization process (order of nanoseconds), high data retention at room temperature (over more than ten years), large cyclability (>10 12 times), scalability, and an excellent contrast in terms of optical reflectivity and electrical resistivity between the amorphous and crystalline states that allow to populate the intermediate states. [12][13][14][15][16][17] Currently, chalcogenide-based PCMs are already being applied in commercial optical storage media such as CDs, DVDs, and Blu-ray disks. [16] At the same time, the reversible electrical resistivity change of PCMs can be applied in nonvolatile electronic memory, which is considered to succeed FLASH memory technology and is becoming the most promising candidate for future data storage technology. [17] Realization of multilevel states in Ge-Sb-Te-based materials is a promising response to the performance improvements in commercialization of PCMs regarding above optical and solid state memory devices, but it is also central for applications in reconfigurable photonic devices, arithmetic processes, logic and neuromorphic computing. [5,9,[18][19][20][21] In order to realize multilevel states in Ge-Sb-Te-based materials, various approaches have been explored, including either engineering the cell structure/stacking multilayers architecture, or iterative programming techniques. [6][7][8][22][23][24][25] These previous reports on realization of multilevels strategies, however, were mainly focused on the control of the Joule heating dissipation profile in the films which required complex device fabrication processes or extra circuits for varying the amplitude of applied pulses. But due to the fast phase transition in the materials by Multilevel storage techniques are promising for increasing storage density and for reducing energy consumption in the application of phase-change materials based memory devices. However, accurately controlling the phase transitions as well as understanding the underlying switching mechanisms are still under investigation. In this study, nonvolatile optical multilevel switching in single-layered GeTe phase-change films prepared by laser ablation is demons...

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Pulse number control of electrical resistance for multi-level storage based on phase change

Cited by 25 publications

References 17 publications

Vacancy Structures and Melting Behavior in Rock-Salt GeSbTe

Vacancy Structures and Melting Behavior in Rock-Salt GeSbTe

Minimizing MLC PCM write energy for free through profiling-based state remapping

Realization of Multilevel States in Phase‐Change Thin Films by Fast Laser Pulse Irradiation

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