Low-field amorphous state resistance and threshold voltage drift in chalcogenide materials

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

doi:10.1109/ted.2004.825805

Cited by 342 publications

(225 citation statements)

References 16 publications

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“…Up to this point, all theoretical models [12,14,25,29,[50][51][52], while strongly differing in the underlying physical mechanisms, predict an increase in activation energy over time. At the same time, none of these models deals with a potential change in the Arrhenius prefactor yet.…”

Section: Resultsmentioning

confidence: 99%

“…The increase of resistance of phase change memory devices over time has been found to follow the form of a power-law [12]. Furthermore, it is known that the optical bandgap of thin films of amorphous phase change material opens while the resistance drifts [13,14].…”

Section: Introductionmentioning

confidence: 99%

“…In order to connect the resistance increase to changes in the electronic density of states, the valence alternation pair defect model-formerly developed for materials containing chains of chalcogen atoms [24]-has been applied to phase change materials [12]. In their model the authors proposed that upon relaxation neutral defects decay into positively and negatively charged defects resulting in a shift of the Fermi level to midgap and thus an increase in the activation energy of conduction.…”

Section: Introductionmentioning

confidence: 99%

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Role of activation energy in resistance drift of amorphous phase change materials

et al. 2014

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The time evolution of the resistance of amorphous thin films of the phase change materials Ge 2 Sb 2 Te 5 , GeTe and AgIn-Sb 2 Te is measured during annealing at T = 80 • C. The annealing process is interrupted by several fast temperature dips to determine the changing temperature dependence of the resistance. This procedure enables us to identify to what extent the resistance increase over time can be traced back to an increase in activation energy E A or to a rise of the prefactor R * . We observe that, depending on the material, the dominating contribution to the increase in resistance during annealing can be either a change in activation energy (Ge 2 Sb 2 Te 5 ) or a change in prefactor (AgIn-Sb 2 Te). In the case of GeTe, both contribute about equally. We conclude that any phenomenological model for the resistance drift in amorphous phase change materials that is based on the increase of one parameter alone (e.g., the activation energy) cannot claim general validity.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Role of activation energy in resistance drift of amorphous phase change materials

et al. 2014

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“…To get rid of the drift effect [32], the delay between the different pulses is constant. The impact of the ambient temperature is studied and error bars are obtained by repeating three times the exact same set of measurements.…”

Section: Electrical Characterization Methodsmentioning

confidence: 99%

Comprehensive Phase-Change Memory Compact Model for Circuit Simulation

Pigot

Bocquet

Gilibert

et al. 2018

IEEE Trans. Electron Devices

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Abstract-In this paper, a new continuous multilevel compact model for phase-change memory (PCM) is proposed. It is based on modified rate equations with the introduction of a variable related to GST melting. The model is evaluated using a large set of dynamic measurements and shows a good accuracy with a single model card. All fitting parameters are discussed and their impacts are detailed. Full circuit simulation is performed. Good convergence and fast simulation time suggest that this new compact model can be exploited for PCM circuit design.

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“…8,10 A recent study reported that different crystallinity of passive GST component results in different switching behaviors. 10 To date, major efforts in PCRAM research have been focused on scalability, [11][12][13] endurance, 13 resistance drift, 14,15 switching speeds and the discovery of new materials. 16 In the case of GST-based PCRAM, the critical issue involves the reliable and durable switching operation of nanometer-scale switching volumes.…”

Section: Introductionmentioning

confidence: 99%

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM

et al. 2015

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Phase-change random access memory (PCRAM) is one of the most promising nonvolatile memory devices. However, inability to secure consistent and reliable switching operations in nanometer-scale programing volumes limits its practical use for highdensity applications. Here, we report in situ transmission electron microscopy investigation of the DC set switching of Ge-Sb-Te (GST)-based vertical PCRAM cells. We demonstrate that the microstructure of GST, particularly the passive component surrounding the dome-shaped active switching volume, plays a critical role in determining the local temperature distribution and is therefore responsible for inconsistent cell-to-cell switching behaviors. As demonstrated by a PCRAM cell with a highly crystallized GST matrix, the excessive Joule heat can cause melting and evaporation of the switching volume, resulting in device failure. The failure occurred via two-step void formation due to accelerated phase separation in the molten GST by the polaritydependent atomic migration of constituent elements. The presented real-time observations contribute to the understanding of inconsistent switching and premature failure of GST-based PCRAM cells and can guide future design of reliable PCRAM. INTRODUCTIONPhase-change random access memory (PCRAM) devices store and erase information by utilizing a large resistivity difference between the crystalline and amorphous states of chalcogenide materials. 1 Among various chalcogenide materials, the Ge-Sb-Te (GST) alloy system is currently considered the most promising candidate material for PCRAM owing to its fast and reversible phase-transition capability, in both the amorphous-to-crystalline (set) and the reverse crystallineto-amorphous (reset) switching. 2,3 Moreover, the set switching of GST occurs through an abrupt increase in the current density at a critical electric field, which is known as threshold switching. 1,4 The threshold switching provides local Joule heat and thereby facilitates the crystallization process at a relatively low electric field, ranging from 30 to 50 V μm − 1 . 5,6 Many modern PCRAM cell designs adopt a nanometer-scale hemispherical or cylindrical shape for programing volume to increase the cell density and reduce the operation power. 7 In such device structures, only a portion of the programing volume makes direct contact with a heater electrode, and the other sides are surrounded by passive GST that remains in the crystalline state and acts as an electrical conductivity path during the set and reset switching. One of the critical reliability issues related to these cell structures is the compositional change, or phase separation, caused by electric field-

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Low-field amorphous state resistance and threshold voltage drift in chalcogenide materials

Cited by 342 publications

References 16 publications

Role of activation energy in resistance drift of amorphous phase change materials

Role of activation energy in resistance drift of amorphous phase change materials

Comprehensive Phase-Change Memory Compact Model for Circuit Simulation

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM

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