Modeling of Phase-Change Memory: Nucleation, Growth, and Amorphization Dynamics During Set and Reset: Part I—Effective Media Approximation

Woods, Zachary; Gokirmak, Ali

doi:10.1109/ted.2017.2745506

Cited by 24 publications

(29 citation statements)

References 38 publications

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“…We model phase change similarly as in Woods et. al 2,3 , which we briefly describe here before discussing updates that…”

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confidence: 99%

“…We model temperature and grain size dependent phase change velocities in Ge2Sb2Te5 (GST), a common phase change material, based on kinetic and thermodynamic parameters. We incorporate heterogeneous melting into a finite element phase change model coupled with electrothermal physics [2][3][4][5][6][7] and show that it can account for the experimentally demonstrated PCM performance improvement with decreasing grain size 8,9 .…”

mentioning

confidence: 99%

“…We model phase change similarly as in Woods et. al 2,3 , which we briefly describe here before discussing updates that Fig. 3: (a) The integral of accounts for the difference in the latent heats of fusion and crystallization (Δhlc(916 K) = 128.9 J/g and Δhlc(431 K) = 34.2 J/g, respectively 22 ).…”

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confidence: 99%

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Modeling heterogeneous melting in phase change memory devices

Scoggin

Woods

Silva

et al. 2019

Applied Physics Letters

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We present thermodynamic crystallization and melting models and calculate phase change velocities in Ge2Sb2Te5 based on kinetic and thermodynamic parameters. The calculated phase change velocities are strong functions of grain size, with smaller grains beginning to melt at lower temperatures. Phase change velocities are continuous functions of temperature which determine crystallization and melting rates. Hence, set and reset times as well as power and peak current requirements for switching are strong functions of grain size. Grain boundary amorphization can lead to a sufficient increase in cell resistance for small-grain phase change materials even if the whole active region does not completely amorphize. Isolated grains left in the amorphous regions, the quenched-in nuclei, facilitate templated crystal growth and significantly reduce set times for phase change memory cells. We demonstrate the significance of heterogeneous melting through 2-D electrothermal simulations coupled with a dynamic materials phase change model. Our results show reset and set times on the order of ~1 ns for 30 nm wide confined nanocrystalline (7.5 nm -25 nm radius crystals) phase change memory cells.Solids tend to melt heterogeneously: the liquid phase initially forms at high energy sites such as grain boundaries and material interfaces. While many materials heat ~20% above their melting temperature (Tmelt) before the liquid phase forms within the bulk solid, heterogeneous melting may occur below Tmelt 1 . In this manuscript, we consider the impacts of heterogeneous melting on phase change memory (PCM). PCM is a non-volatile memory technology which stores information as the low resistivity crystalline or high resistivity amorphous phase of a material (Fig. 1). PCM retention, endurance, and speed depend on the physics underlying crystallization and melting. We model temperature and grain size dependent phase change velocities in Ge2Sb2Te5 (GST), a common phase change material, based on kinetic and thermodynamic parameters. We incorporate heterogeneous melting into a finite element phase change model coupled with electrothermal physics 2-7 and show that it can account for the experimentally demonstrated PCM performance improvement with decreasing grain size 8,9 .Tmelt is the temperature at which the Gibbs free energy difference between bulk liquid and crystalline phases (Δglc) is zero. However, melting becomes thermodynamically favorable below Tmelt at crystal interfaces. The Gibbs free energy of a spherical crystal surrounded by liquid (ΔGcrys) is calculated by classical nucleation theory aswhere r is the crystal radius and γlc is the energy penalty at a liquid-crystal interface (Fig. 2a). (1) has extrema at r = 0 and r = rc, the critical radius:(2) Crystals with r < rc are subcritical and can reduce ΔGcrys by shrinking, i.e. melting. rc increases with T: Δglc decreases with increasing T, crossing 0 at Tmelt. γlc is difficult to measure in GST and often used as a fitting parameter; however, γlc increases with T in metals as well as in t...

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“…We model phase change similarly as in Woods et. al 2,3 , which we briefly describe here before discussing updates that…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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Modeling heterogeneous melting in phase change memory devices

Scoggin

Woods

Silva

et al. 2019

Applied Physics Letters

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“…In this paper we use the classical nucleation and growth theory (effective media) . [ 43 ] to simulate the crystallization fraction of the GSST. Because of the existence of a nucleation‐dominated in the crystallization mechanism, it seems challenging to fully crystallize the GSST inside the 1D gold grating by a single nanosecond shot pulse from the as‐deposited amorphous state.…”

Section: Heat Transfer and Photo‐thermal Effectmentioning

confidence: 99%

Temporal Analysis of Photo‐Thermally Induced Reconfigurability in a 1D Gold Grating Filled with a Phase Change Material

Zamani

Hatef

Nadgaran

2021

Advcd Theory and Sims

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In this study, the finite‐element method is used to numerically calculate a photo‐thermally induced reconfigurability in a 1D gold grating structure filled with the phase change material Ge2Sb2Se4Te1 (GSST). GSST features a reversible and stable phase change between amorphous and crystalline phases around a critical temperature of 410 K with broadband low optical loss. In this study, the required heating for the transition between phases is provided by a nanosecond Gaussian pulse laser through a photo‐thermal absorption process. A comprehensive heat transfer analysis is performed to investigate the thermal characterizations of the proposed structure. The results show that in the amorphous state, the structure has a near unity absorption band in the infrared region. As the temperature increases during the pulse, the GSST undergoes the amorphous to crystalline phase change. In the intermediate states (partial crystallization) of the GSST two resonance peaks are excited and the absorption finally reaches its minimum value of 0.2 in the GSST crystalline phase. The findings of this study not only provide the fundamental concepts for the suggested tunable structure, but also have potential applications in a variety of nanophotonic devices including thermal emission controllers, sensors, and optical detection devices.

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“…[18] All RRAM devices experience joule heating, [19][20][21][22][23][24] electrical breakdown, [25] thermal transport, [26,27] thermoelectric effects, [19,20,28,29] electromigration, [30,31] and percolation transport, [16,17,32] which make them harder to model compared with conventional electronic devices. [33][34][35][36][37] However, their compatibility with backend-of-the-line low-temperature processing makes them very attractive.…”

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confidence: 99%

Phase‐Change Logic via Thermal Cross‐Talk for Computation in Memory

Kan'an

Khan

Woods

et al. 2020

Physica Rapid Research Ltrs

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Herein, logic function implementations are computationally demonstrated using lateral and vertical multicontact phase‐change devices integrated with complementary metal–oxide–semiconductor (CMOS) circuitry, which use thermal cross‐talk as a coupling mechanism to implement logic functions at smaller CMOS footprints. Thermal cross‐talk during the write operations is utilized to recrystallize the previously amorphized regions to achieve toggle operations. Amorphized regions formed between different pairs of write contacts are utilized to isolate read contacts. Typical expected reduction in CMOS footprint is ≈50% using the described approach for toggle‐multiplexing, JK‐multiplexing, and 2 × 2 routing. The switching speeds of the phase‐change devices are in the order of nanoseconds and are inherently nonvolatile. An electrothermal modeling framework with dynamic materials models is used to capture the device dynamics, and current and voltage requirements.

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Modeling of Phase-Change Memory: Nucleation, Growth, and Amorphization Dynamics During Set and Reset: Part I—Effective Media Approximation

Cited by 24 publications

References 38 publications

Modeling heterogeneous melting in phase change memory devices

Modeling heterogeneous melting in phase change memory devices

Temporal Analysis of Photo‐Thermally Induced Reconfigurability in a 1D Gold Grating Filled with a Phase Change Material

Phase‐Change Logic via Thermal Cross‐Talk for Computation in Memory

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