Evidence of Heat-Assisted Atomic Migration in GeSe Self-Selecting Memory at High Operating Current Density

Herein, the operation of a GeSe ovonic threshold switch (OTS) is studied as a self-selecting memory cell based on the polarity effect. From the observed operating current (Iop) dependence and area scaling behavior, the critical role of Joule heating in ensuring exceptionally large memory window in this material is confirmed. The underlying mechanism is further investigated by means of chemical analysis and is confirmed to be caused by polarity-dependent atomic migration under high-Iop regime, consistent with elemental segregation due to electronegativity contrast. More specifically, selective diffusion of Ge atoms through the TiN layer into negatively biased top electrode stack is observed. At the same time, there is no sign of a similar process for Se atoms under opposite voltage polarity. Based on these observations, a novel memory concept utilizing a selective diffusion barrier is proposed. Furthermore, under low-Iop regime, no major composition change is observed, leaving room for alternative interpretation of the polarity effect under such conditions. Finally, it is demonstrated that functional GeSe OTS-only memory is fabricated with atomic layer deposition, making it suitable for vertical 3D integration to enable low-cost applications. This work investigates the polarity effect in GexSe1-x threshold switches under various operating conditions. The mechanism behind the high-current behavior is elaborated by means of elemental mapping and is shown to be caused by atomic migration within device structure. At the same time, no major composition change is observed at a low operating current.image (c) 2024 WILEY-VCH GmbH