Defects in amorphous phase-change materials

Luckas, Jennifer; Krebs, Daniel; Grothe, S.; Klomfass, J.; Carius, R.; Longeaud, Christophe; Wuttig, Matthias

doi:10.1557/jmr.2013.72

Cited by 46 publications

(41 citation statements)

References 40 publications

(50 reference statements)

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“…Our measurements of thick films enable the determination of the absorption coefficient over a large energy range. They confirm that, on aging, the band gap indeed increases, consistent with previous PDS 44 and ellipsometry data 43 . In addition, the PDS data in Fig.…”

Section: Resultssupporting

confidence: 90%

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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Section: Resultssupporting

confidence: 90%

Aging mechanisms in amorphous phase-change materials

et al. 2015

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“…Furthermore, it has been shown that after accelerated drift by annealing, the band gap is increased, 12,24 while the shape of the temperature dependence is preserved. 25 In particular for GeTe, an increase of the band gap upon annealing at 413 K by about 9% has been measured. 25 Based on these findings, the temperature dependent resistance shown in Fig.…”

Section: Discussionmentioning

confidence: 98%

“…25 In particular for GeTe, an increase of the band gap upon annealing at 413 K by about 9% has been measured. 25 Based on these findings, the temperature dependent resistance shown in Fig. 3(a) has been modeled using Eqs.…”

Section: Discussionmentioning

confidence: 98%

The influence of resistance drift on measurements of the activation energy of conduction for phase-change material in random access memory line cells

Oosthoek

Krebs

Salinga

et al. 2012

Journal of Applied Physics

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Temporal drift of the amorphous resistance in phase-change random access memory (PRAM) is a temperature accelerated process. Increasing the temperature will speed up the drift process which is shown to affect measurements of the activation energy of conduction (Ea, slope of log(R) versus 1/kT). Doped SbTe phase change (PRAM) line cells were brought to the amorphous state and were subjected to annealing experiments. First, it is shown that when the temperature is increased by a fixed rate, the resistance does not follow a unique function of temperature but depends on the heating rate. This can be attributed to resistance drift taking place during the ramp. Upon cooling, the drift process freezes and only then physically relevant, i.e., time independent, values for Ea can be obtained, because of the absence of additional drift. The observed increase in resistance as a function of annealing history (for various frozen-in drift levels) is modeled and well-reproduced using a trap limited band transport model. The model explains these observations by an increase of the temperature dependent band gap by about 47 meV due to drift at 418 K. V

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“…The drift and the noise behavior have both been attributed to the large defect distributions within the amorphous phase that dominate the transport behavior [11][12][13][14][15][16]. In this study, we establish a link between the changes in the electrical resistance upon drift and changes in the electronic density of states (DoS).…”

Section: Introductionmentioning

confidence: 88%

Changes in electrical transport and density of states of phase change materials upon resistance drift

et al. 2014

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Phase-change memory technology has become more mature in recent years. But some fundamental problems linked to the electrical transport properties in the amorphous phase of phase-change materials still need to be solved. The increase of resistance over time, called resistance drift, for example, poses a major challenge for the implementation of multilevel storage, which will eventually be necessary to remain competitive in terms of high storage densities. To link structural properties with electrical transport, a broader knowledge of (i) changes in the density of states (DoS) upon structural relaxation and (ii) the influence of defects on electrical transport is required. In this paper, we present temperaturedependent conductivity and photo-conductivity measurements on the archetype phase change material GeTe. It is shown that trap-limited band transport at high temperatures (above 165 K) and variable range hopping at low temperatures are the predominating transport mechanism. Based on measurements of the temperature dependence of the optical band gap, modulated photo-conductivity and photo-thermal deflection spectroscopy, a DoS model for GeTe was proposed. Using this DoS, the temperature dependence of conductivity and photo-conductivity has been simulated. Our work shows how changes in the DoS (band gap and defect distributions) will affect the electrical transport before and after Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.temperature-accelerated drift. The decrease in conductivity upon annealing can be explained entirely by an increase of the band gap by about 12%. However, low-temperature photo-conductivity measurements revealed that a change in the defect density may also play a role. New J. Phys. 16 (2014) 043015 D Krebs et al New J. Phys. 16 (2014) 043015 D Krebs et al New J. Phys. 16 (2014) 043015 D Krebs et al 7 New J. Phys. 16 (2014) 043015 D Krebs et al 8

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Defects in amorphous phase-change materials

Cited by 46 publications

References 40 publications

Aging mechanisms in amorphous phase-change materials

Aging mechanisms in amorphous phase-change materials

The influence of resistance drift on measurements of the activation energy of conduction for phase-change material in random access memory line cells

Changes in electrical transport and density of states of phase change materials upon resistance drift

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