Engineering grains of Ge&lt;inf&gt;2&lt;/inf&gt;Sb&lt;inf&gt;2&lt;/inf&gt;Te&lt;inf&gt;5&lt;/inf&gt; for realizing fast-speed, low-power, and low-drift phase-change memories with further multilevel capabilities

Wang, W. J.; Loke, Desmond K.; Law, L. T.; Shi, Lu; Zhao, Rong; Li, Minghua; Chen, L. L.; Yang, Hongxin; Yeo, Yee-Chia; Adeyeye, A. O.; Chong, Tow Chong; Lacaita, A.L.

doi:10.1109/iedm.2012.6479143

Cited by 13 publications

(10 citation statements)

References 7 publications

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“…Wang et. al 8 experimentally showed a trend of decreased reset and set times as radii decreased from 8.5 nm to 5 nm but achieved sub-nanosecond reset while requiring ~50 ns for set. The longer reset and shorter set times in our simulations are consistent with a v∞ that underestimates melting velocities but overestimates crystallization velocities, resulting in less melting during reset, more crystallization while cooling after reset, and faster crystallization during set.…”

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confidence: 98%

“…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 .…”

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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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confidence: 98%

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confidence: 99%

Modeling heterogeneous melting in phase change memory devices

Scoggin

Woods

Silva

et al. 2019

Applied Physics Letters

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“…(II) Initialization electrical pulse : a weak incubation voltage pulse (~0.3 V at 10 ns) on GST can help to pre-form fourfold membered atomic rings, which are the precursors for distorted octahedrons in rocksalt c-GST 5 6 . (III) Diminishing grain size : as the grain size of the GST is reduced from 17 to 13 nm, the Set time can be reduced from 44 to 40 ns 7 8 . In contrast, reducing the Reset power can not only prolong PCM cell life to compete with DRAM (>10 15 cycles) 3 , but can also effectively lower the standards for drive capability of gating device to achieve high-density integration 9 10 .…”

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confidence: 99%

One order of magnitude faster phase change at reduced power in Ti-Sb-Te

et al. 2014

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To date, slow Set operation speed and high Reset operation power remain to be important limitations for substituting dynamic random access memory by phase change memory. Here, we demonstrate phase change memory cell based on Ti0.4Sb2Te3 alloy, showing one order of magnitude faster Set operation speed and as low as one-fifth Reset operation power, compared with Ge2Sb2Te5-based phase change memory cell at the same size. The enhancements may be rooted in the common presence of titanium-centred octahedral motifs in both amorphous and crystalline Ti0.4Sb2Te3 phases. The essentially unchanged local structures around the titanium atoms may be responsible for the significantly improved performance, as these structures could act as nucleation centres to facilitate a swift, low-energy order-disorder transition for the rest of the Sb-centred octahedrons. Our study may provide an alternative to the development of high-speed, low-power dynamic random access memory-like phase change memory technology.

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“…The suppressed peaks and the smaller grain size could be indicated the incorporated W atom plays a role in suppressing crystallization of the Sb 3 Te films, which correspond to the increased T c and E a of W x Sb 3 Te films. In practical applications, the smaller grain could reduce the power consumption of the cell device [17].…”

Section: Methodsmentioning

confidence: 99%