Electronic Switching in Phase-Change Memories

Pirovano, A.; Lacaita, A.L.; Benvenuti, A.; Pellizzer, F.; Bez, R.

doi:10.1109/ted.2003.823243

Cited by 583 publications

(385 citation statements)

References 37 publications

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“…However, we see that the form is relatively simple, being in marked contrast to the switching behavior observed in the crystallization process. 5,9,10 In addition, in the 100 ns result ͑b͒, the current tends to increase with time, which may correspond to the conductivity increase at higher temperatures in the fcc Ge 2 Sb 2 Te 5 . 13 Mark erasure has also been examined for the mound and ring types.…”

Section: A Afmmentioning

confidence: 92%

Nanoscale phase changes in crystalline Ge2Sb2Te5 films using scanning probe microscopes

Satoh

Sugawara

Tanaka

2006

Journal of Applied Physics

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Nanoscale amorphous marks have been produced in crystalline Ge 2 Sb 2 Te 5 films using an atomic-force microscope ͑AFM͒ and a scanning-tunneling microscope ͑STM͒ through electrical phase changes. Voltage pulses with duration of 5-100 ns applied by metal probes of the AFM and the STM can produce, respectively, high-resistance regions and deformations, the smallest sizes being ϳ10 and ϳ100 nm in diameter. Raman-scattering spectra demonstrate that these marks are amorphous. The AFM mark can be erased by applying longer pulses. Formation processes of the marks are considered from electrothermal and thermodynamic aspects.

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Section: A Afmmentioning

confidence: 92%

Nanoscale phase changes in crystalline Ge2Sb2Te5 films using scanning probe microscopes

Satoh

Sugawara

Tanaka

2006

Journal of Applied Physics

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“…The threshold switching voltage is linked to the amorphous thickness by 22 V th ðtÞ ¼ E th ðtÞÁu a ðtÞ: ð14Þ E th denotes the threshold switching field at which the electronic threshold switching takes place. At this critical field, the resistance of the PCM cell drops to a substantially lower value, resulting in a sharp increase in the current 45,46 . However, E th (t) itself undergoes an evolution with time owing to the structural relaxation of the amorphous phase.…”

Section: Methodsmentioning

confidence: 99%

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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“…The crystalline GST has acceptor like traps due to vacancies whereas the amorphous phase has both donor like and acceptor like traps due to dangling bonds in the Te sites. According to a model by Pirovano et al 6 impact ionization leads to recombination in the shallow donor like traps pushing the electron quasifermi level closer to the conduction The reset operation is performed by applying pulse amplitudes large enough for the GST to be locally heated above its melting point (~620 ˚C) and then super-cooling (melt-quenching) it below its glass transition temperature (~300 ˚C) into the amorphous phase. The switching back to the crystalline state can be achieved by sweeping the dc bias beyond the snap-back voltage as Figure 4 displays repeated measurements of the pulsed reset operation to prepare a 75 nm circular device in the amorphous phase.…”

Section: Device Structure and I-v Characteristicsmentioning

confidence: 99%

Electrical switching dynamics in circular and rectangular Ge2Sb2Te5 nanopillar phase change memory devices

Ozatay

Stipe

Katine

et al. 2008

Journal of Applied Physics

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We have measured the critical phase change conditions induced by electrical pulses in Ge 2 Sb 2 Te 5 nanopillar phase change memory devices by constructing a comprehensive resistance map as a function of pulse parameters (width, amplitude and trailing edge). Our measurements reveal that the heating scheme and the details of the contact geometry play the dominant role in determining the final phase composition of the device such that a non-uniform heating scheme using rectangular contacts promotes partial amorphization/crystallization for a wide range of pulse parameters enabling multiple resistance levels for data storage applications. Furthermore we find that fluctuations in the snap-back voltage and set/reset resistances in repeated switching experiments are related to the details of the current distribution such that a uniform current injection geometry (i.e. circular contact) favors more reproducible switching parameters. This shows that possible geometrical defects in nanoscale phase change memory devices may play an essential role in the performance of the smallest possible devices through modification of the exact current distribution in the active chalcogenide layer. We present a three-dimensional finite element model of the electro-thermal physics to provide insights into the underlying physical mechanisms of the switching dynamics as well as to quantitatively account for the scaling behaviour of the switching currents in both circular and rectangular contact geometries. The calculated temporal evolution of the heat distribution within the pulse duration shows distinct features in rectangular contacts providing evidence for locally hot spots at the sharp corners of the current injection site due to current crowding effects leading to the observed behaviour.

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Electronic Switching in Phase-Change Memories

Cited by 583 publications

References 37 publications

Nanoscale phase changes in crystalline Ge2Sb2Te5 films using scanning probe microscopes

Nanoscale phase changes in crystalline Ge2Sb2Te5 films using scanning probe microscopes

Crystal growth within a phase change memory cell

Electrical switching dynamics in circular and rectangular Ge2Sb2Te5 nanopillar phase change memory devices

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