Atomistic Insight on the Threshold Switching Mechanism in Innovative Amorphous Chalcogenide Thin Films Used in Advanced OTS Selector Devices

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Atomistic Insight on the Threshold Switching Mechanism in Innovative Amorphous Chalcogenide Thin Films Used in Advanced OTS Selector Devices

Pierre Noe1,Anthonin Verdy1,Jean-Yves Raty2,Francesco d'Acapito3,Gabriele Navarro1,Françoise Hippert4,Jérôme Gaudin5,Mathieu Bernard1

Université Grenoble-Alpes, CEA-LETI1,FNRS-Liège University2,CNR-IOM-OGG c/o ESRF3,LNCMI (CNRS, Université Grenoble Alpes, UPS, INSA)4,Centre Lasers Intenses et Applications5

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Chalcogenide materials exhibit a unique portfolio of properties which has led to their wide use for non-volatile memory applications such as optical data storage or more recently Phase-Change Random Access Memory [1]. Chalcogenide glasses (CGs) exhibit a high transparency window in the IR range and large optical nonlinearities offering unique opportunities for elaboration of innovative mid-IR components [2]. Besides, a huge nonlinear behavior of conductivity is observed in some CGs under electrical field application. Such CGs appear to be promising materials for innovative OTS (Ovonic Threshold Switching) selector elements in 3D resistive memory arrays [3]. Indeed, among the different selector technologies developed in the last years [4], the OTS selector technology showed the capability to overcome key issues for crossbar application, as very recently demonstrated in the Intel/Micron OptaneTM memory technology [5]. The OTS mechanism discovered in the 60’s [6] consists in the switching between a high resistance (OFF state) and a low resistance state (ON state) when the voltage applied on the CG exceeds a critical value (threshold voltage Vth). When the current is reduced below the holding current density, Jh, the selector recovers its high resistance state. However, the underlying physical mechanism is still under debate with, up to now, two main classes of models, one involving a purely electronic effect [7] and the other invoking structural changes under field application [8]. In that context, we investigate the origin of the OTS effect by means of a structural analysis of some prototypical and state-of-the-art Ge/Sb/Se-based OTS glasses. The structure of selected thin films, differing significantly by the amplitude of the OTS effect and the performance of OTS devices, is studied by means of Fourier Transform Infrared (FTIR) and Raman spectroscopy as well as X-Ray Absorption Spectroscopy. As a result, we elucidate the role of Sb and N doping in changing the structure of Ge30Se70 glass, which leads to improved OTS selector performance. Finally, from this structural analysis and original ab initio molecular dynamics simulations, we will propose a new scenario explaining the origin of the OTS mechanism in such state-of-the-art CGs.

References
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[5] http://www.techinsights.com/about-techinsights/overview/blog/intel-3D-xpoint-memory-die-removed-from-intel-optane-pcm/
[6] S. R. Ovshinsky, Phys. Rev. Lett. 21 (20), 1968.
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