Ultrafast Characterization of Phase-Change Material Crystallization Properties in the Melt-Quenched Amorphous Phase

Jeyasingh, Rakesh; Fong, Scott W.; Lee, Jae-Ho; Li, Zijian; Chang, Kuo‐Wei; Mantegazza, D.; Asheghi, Mehdi; Goodson, Kenneth E.; Wong, H.-S. Philip

doi:10.1021/nl500940z

Cited by 110 publications

(93 citation statements)

References 34 publications

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“…We postulate that this results in fewer clusters that can act as precursors of crystalline nuclei, thus making nucleation more difficult. That the activation energy for growth is unaffected by the deposition conditions may explain why it has been found in other studies that samples having the same composition but made under different conditions have the same temperature dependence for crystallization, while differences in the crystallization rate are still observed due to differences in the nucleation rates [32,33]. Figure 5 shows Raman spectra for GeTe films deposited at different temperatures.…”

Section: Resultsmentioning

confidence: 85%

Impact of deposition conditions on the crystallization kinetics of amorphous GeTe films

et al. 2015

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The speed at which phase change memory devices can operate depends strongly on the crystallization kinetics of the amorphous phase. To better understand factors that affect the crystallization rate, we have investigated crystallization of GeTe films as a function of their deposition temperatures and deposition rates, using X-ray synchrotron radiation and Raman spectroscopy. As-deposited films were found to be fully amorphous under all conditions, even though films deposited at higher temperatures and lower rates experienced lower effective quench rates. Non-isothermal transformation curves show that the apparent crystallization temperature of GeTe films decreases with increasing deposition temperature and decreasing deposition rate. It was found that this correlates with a decrease in the activation energy for nucleation (calculated using Kissinger's analysis), while the activation energy for crystal growth remained unaffected. From Raman spectroscopy measurements, it was found that increasing the deposition temperature or decreasing the deposition rate, and therefore the effective quench rate, reduces the number of homopolar Te-Te bonds and thereby reduces the barrier to crystal nucleation.

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Section: Resultsmentioning

confidence: 85%

Impact of deposition conditions on the crystallization kinetics of amorphous GeTe films

et al. 2015

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“…The steep slope of run2 indicates a speed of the order of 1 m/s once the subcritical phase has been passed, which is less than measured in recent differential scanning calorimetry (DSC) at 600 K (2.5-3.0 m/s) [13]. Recent measurements for melt-quenched PRAM cells have reported much slower rates up to 580 K [31]. Simulations run1-run3 show a clear plateau before crystallization and differ from run0, which starts to evolve immediately.…”

Section: B Samples Without History Of Order: Run1run2run3mentioning

confidence: 76%

Simulation of crystallization inGe2Sb2Te5: A memory effect in the canonical phase-change material

2014

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Crystallization of amorphous Ge 2 Sb 2 Te 5 (GST) has been studied using four extensive (460 atoms, up to 4 ns) density functional/molecular dynamics simulations at 600 K. This phase change material is a rare system where crystallization can be simulated without adjustable parameters over the physical time scale, and the results could provide insight into order-disorder processes in general. Crystallization is accompanied by an increase in the number of ABAB squares (A: Ge, Sb; B: Te), percolation, and the occurrence of low-frequency localized vibration modes. A sample with a history of order crystallizes completely in 1.2 ns, but ordering in others was less complete, even after 4 ns. The amorphous starting structures without memory display phases (>1 ns) with subcritical nuclei (10-50 atoms) ranging from nearly cubical blocks to stringlike configurations of ABAB squares and AB bonds extending across the cell. Percolation initiates the rapid phase of crystallization and is coupled to the directional p-type bonding in metastable GST. Cavities play a crucial role, and the final ordered structure is distorted rock salt with a face-centered cubic sublattice containing predominantly Te atoms. We comment on earlier models based on smaller and much shorter simulations.

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“…In particular, chalcogenide-based PCMs have the ability to switch between these two states in response to appropriate heat stimuli (crystallization) or melt-quenching processes (amorphization) 17 . These PCMs, mainly tellurides and antimonides, can be switched on a subnanosecond timescale 15,18 with high reproducibility which enables ultra-fast operation over switching cycles up to 10 12 times 14,16 using current-generation materials (with new and improved materials, such as the so-called phase-change super-lattice materials 19 , expected to deliver even better performance in the future). In addition, at normal operating temperatures the states are highly stable for years 15,20 , a key requirement for a truly nonvolatile memory.…”

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confidence: 99%

Integrated all-photonic non-volatile multi-level memory

et al. 2015

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Rios, Stegmaier et al., Integratable all-photonic nonvolatile multi-level memory Integratable all-photonic nonvolatile multi-level memoryWe show that individual memory elements can be addressed using a wavelength multiplexing scheme. Our multi-level, multi-bit devices provide a pathway towards eliminating the von-Neumann bottleneck and portend a new paradigm in all-photonic memory and non-conventional computing.* These authors contributed equally.-2-The advent of photonic technologies, in particular in the area of optical signaling, coupled with advances made in nanofabrication capabilities has created a growing need for practical allphotonic memories 3,[7][8][9][10] . Such memories are essential to supercharge computational performance in serial computers by speeding up the von-Neumann bottleneck, i.e. the information traffic jam between the processor and the memory. This bottleneck limits the speed of almost all processors today; it has already led to the introduction of multicore processor architectures and drives the search for viable on-chip optical interconnects. However, shuttling information optically from the processor to electronic memories is presently not efficient because electrical signals have to be converted to optical ones and vice-versa. Instead, information transfer and storage exclusively by optical means is highly desirable because of the inherently large bandwidth 1,3 , low residual cross-talk and high speed of optical information transfer. On a chip this has been challenging to achieve because practical photonic memories would need to retain information for long periods of time and require full-integration with the ancillary electronic circuitry, thus requiring compatibility with semiconductor processing 11.Ideal candidates for all-optical memories are phase-change materials (PCMs), already the subject of intense research and development over the last decade, but in the context of electronic memories [12][13][14] . A striking and functional feature of these materials is the high contrast between the crystalline and amorphous phase of both their electrical and optical properties 15,16 . In particular, chalcogenide-based PCMs have the ability to switch between these two states in response to appropriate heat stimuli (crystallization) or melt-quenching processes down to nanoscale cell sizes, which enables dense packaging and low-power memory switching. In our devices, data is stored in a nanoscale GST cell placed directly on top of a nanophotonic waveguide. Both writing into the memory cell and read-out of the stored information is carried out via evanescent coupling to the phase-change material and is thus not subject to the diffraction limit; because this is done directly within the waveguide using nanosecond optical pulses, our approach provides a promising route towards fast all-optical data storage in photonic circuits.The geometry of our memory cell and the operating principle is shown schematically in Fig. 1a. We store information in the GST (yellow region) by employing evanescent coup...

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Ultrafast Characterization of Phase-Change Material Crystallization Properties in the Melt-Quenched Amorphous Phase

Cited by 110 publications

References 34 publications

Impact of deposition conditions on the crystallization kinetics of amorphous GeTe films

Impact of deposition conditions on the crystallization kinetics of amorphous GeTe films

Simulation of crystallization inGe2Sb2Te5: A memory effect in the canonical phase-change material

Integrated all-photonic non-volatile multi-level memory

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