On the key role of oxygen vacancies electromigration in the memristive response of ferroelectric devices

Abstract

Ferroelectric memristors are intensively studied due to their potential implementation in data storage and processing devices. In this work we show that the memristive behavior of metal/ferroelectric oxide/metal devices relies on the competition of two effects: the modulation of metal/ferroelectric interface barriers by the switchable ferroelectric polarization and the electromigration of oxygen vacancies, with the depolarizing field playing a fundamental role in the latter. We simulate our experimental results with a phenomenological model that includes both effects and we reproduce several non-trivial features of the electrical response, including resistance relaxations observed after external poling. Besides providing insight into the underlying physics of these complex devices, our work suggests that it is possible to combine non-volatile and volatile resistive changes in single ferroelectric memristors, an issue that could be useful for the development of neuromorphic devices.

Reversible oxygen migration and phase transitions in hafnia-based ferroelectric devices

“…Here we report operando atomic scale electron microscopy investigations of the behavior of LSMO/HZO/LSMO capacitor stacks grown on conducting (Nb-doped) STO substrate under electric field (see materials and methods in SI). LSMO is a standard choice of bottom electrode in complex oxide devices (23)(24)(25)(26)31) and, thus, the findings reported here are relevant for understanding a wider class of devices. In situ biasing measurements were performed while employing at the same time two scanning transmission electron microscopy (STEM) imaging modes: high-angle annular dark-field (HAADF) STEM and integrated differential phase contrast (iDPC) STEM.…”

“…More generally, in devices of thin-film ferroelectric oxides such as tunnel junctions, both V ̈o migration and polarization switching lead to memristive hysteresis (22)(23)(24)(25)(26)(27). Understanding whether these effects are synergetic or independent is crucial to achieve device control, and is a topic of active research (29)(30)(31)(32)(33). In tunnel junctions of HZO thin-films on LSMO buffered SrTiO3 (STO), Wei et al (22) observed a divergence of the tunnel electro-resistance (TER) from 100% to 10 6 %, upon device cycling, which was explained as a possible transition from polarization switching to V ̈o migration assisted switching, suggesting the independence of the two mechanisms.…”