Recovery and Drift Dynamics of Resistance and Threshold Voltages in Phase-Change Memories

Ielmini, Daniele; Lacaita, A.L.; Mantegazza, D.

doi:10.1109/ted.2006.888752

Cited by 237 publications

(183 citation statements)

References 17 publications

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“…This is unlike samples produced by sputter deposition. Hence, one of the biggest blessings (the fast speed of the materials) also leads to the biggest curse of the technology, namely, the structural relaxation towards the equilibrium that is observed in our work and in literature as drift in growth rate, threshold voltage and resistance 37 . In particular, the last is a significant challenge in realizing multi-level storage 31,38 .…”

Section: Discussionsupporting

confidence: 50%

Crystal growth within a phase change memory cell

2014

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In spite of the prominent role played by phase change materials in information technology, a detailed understanding of the central property of such materials, namely the phase change mechanism, is still lacking mostly because of difficulties associated with experimental measurements. Here, we measure the crystal growth velocity of a phase change material at both the nanometre length and the nanosecond timescale using phase-change memory cells. The material is studied in the technologically relevant melt-quenched phase and directly in the environment in which the phase change material is going to be used in the application. We present a consistent description of the temperature dependence of the crystal growth velocity in the glass and the super-cooled liquid up to the melting temperature.

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Section: Discussionsupporting

confidence: 50%

Crystal growth within a phase change memory cell

2014

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“…PCMs are used as the active part of non-volatile memory devices 5,6 , which exploit the fast and reversible switch between a conductive crystalline structure and an amorphous phase that displays a higher electrical resistivity. On aging, the resistivity of the amorphous state for a large number of such systems [7][8][9] increases even further. This 'resistance drift' impedes the realization of multilevel memories.…”

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confidence: 99%

Aging mechanisms in amorphous phase-change materials

et al. 2015

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Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance spectroscopy experiments. We show that aging is accompanied by a progressive change of the local chemical order towards the crystalline one. Yet, the glass evolves towards a covalent amorphous network with increasing Peierls distortion, whose structural and electronic properties drift away from those of the resonantly bonded crystal. This behaviour sets phase-change materials apart from conventional glass-forming systems, which display the same local structure and bonding in both phases.

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“…8,10 A recent study reported that different crystallinity of passive GST component results in different switching behaviors. 10 To date, major efforts in PCRAM research have been focused on scalability, [11][12][13] endurance, 13 resistance drift, 14,15 switching speeds and the discovery of new materials. 16 In the case of GST-based PCRAM, the critical issue involves the reliable and durable switching operation of nanometer-scale switching volumes.…”

Section: Introductionmentioning

confidence: 99%

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM

et al. 2015

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Phase-change random access memory (PCRAM) is one of the most promising nonvolatile memory devices. However, inability to secure consistent and reliable switching operations in nanometer-scale programing volumes limits its practical use for highdensity applications. Here, we report in situ transmission electron microscopy investigation of the DC set switching of Ge-Sb-Te (GST)-based vertical PCRAM cells. We demonstrate that the microstructure of GST, particularly the passive component surrounding the dome-shaped active switching volume, plays a critical role in determining the local temperature distribution and is therefore responsible for inconsistent cell-to-cell switching behaviors. As demonstrated by a PCRAM cell with a highly crystallized GST matrix, the excessive Joule heat can cause melting and evaporation of the switching volume, resulting in device failure. The failure occurred via two-step void formation due to accelerated phase separation in the molten GST by the polaritydependent atomic migration of constituent elements. The presented real-time observations contribute to the understanding of inconsistent switching and premature failure of GST-based PCRAM cells and can guide future design of reliable PCRAM. INTRODUCTIONPhase-change random access memory (PCRAM) devices store and erase information by utilizing a large resistivity difference between the crystalline and amorphous states of chalcogenide materials. 1 Among various chalcogenide materials, the Ge-Sb-Te (GST) alloy system is currently considered the most promising candidate material for PCRAM owing to its fast and reversible phase-transition capability, in both the amorphous-to-crystalline (set) and the reverse crystallineto-amorphous (reset) switching. 2,3 Moreover, the set switching of GST occurs through an abrupt increase in the current density at a critical electric field, which is known as threshold switching. 1,4 The threshold switching provides local Joule heat and thereby facilitates the crystallization process at a relatively low electric field, ranging from 30 to 50 V μm − 1 . 5,6 Many modern PCRAM cell designs adopt a nanometer-scale hemispherical or cylindrical shape for programing volume to increase the cell density and reduce the operation power. 7 In such device structures, only a portion of the programing volume makes direct contact with a heater electrode, and the other sides are surrounded by passive GST that remains in the crystalline state and acts as an electrical conductivity path during the set and reset switching. One of the critical reliability issues related to these cell structures is the compositional change, or phase separation, caused by electric field-

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Recovery and Drift Dynamics of Resistance and Threshold Voltages in Phase-Change Memories

Cited by 237 publications

References 17 publications

Crystal growth within a phase change memory cell

Crystal growth within a phase change memory cell

Aging mechanisms in amorphous phase-change materials

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM

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