Abstract
Memristive devices based on electrochemical resistive switching effects have been proposed as promising candidates for in-memory computing and for the realization of artificial neural networks. Despite great efforts toward understanding the nanoionic processes underlying resistive switching phenomena, comprehension of the effect of competing redox processes on device functionalities from the materials perspective still represents a challenge. In this work, we experimentally and theoretically investigate the concurring reactions of silver and moisture and their impact on the electronic properties of a single-crystalline ZnO nanowire (NW). A decrease in electronic conductivity due to surface adsorption of moisture is observed, whereas, at the same time, water molecules reduce the energy barrier for Ag+ ion migration on the NW surface, facilitating the conductive filament formation. By controlling the relative humidity, the ratio of intrinsic electronic conductivity and surface ionic conductivity can be tuned to modulate the device performance. The results achieved on a single-crystalline memristive model system shed new light on the dual nature of the mechanism of how moisture affects resistive switching behavior in memristive devices.
Highlights
Memristive devices based on nanoionic redox processes are considered one of the most promising candidates for the realization of next-generation memories and for the emulation of brain functionalities through the implementation of neuromorphic-type data processing.[1−7] Despite recent breakthroughs in the implementation of neuromorphic algorithms in large memristive networks,[8−12] detailed understanding of the complex redox behavior and of the ionic processes at the single-device level still represents a challenge
Redox-based memristors are two terminal devices in which the functionalities are enclosed in the resistive switching properties of a solid electrolyte, usually a metal-oxide film, sandwiched in between two metal electrodes.[13−17] In the established literature, the switching mechanism is related to nanoionic processes of migration of oxygen species or host metal ions from an electrochemically active electrode, or both.[18]
It is worth noticing that the resistive switching behavior suppressed under dry conditions can be restored by exposing the device again to humidity (Supporting Information S6). All of these results reveal that ionic dynamics underlying resistive switching behavior are strongly influenced by moisture
Summary
Memristive devices based on nanoionic redox processes are considered one of the most promising candidates for the realization of next-generation memories and for the emulation of brain functionalities through the implementation of neuromorphic-type data processing.[1−7] Despite recent breakthroughs in the implementation of neuromorphic algorithms in large memristive networks,[8−12] detailed understanding of the complex redox behavior and of the ionic processes at the single-device level still represents a challenge. Redox-based memristors are two terminal devices in which the functionalities are enclosed in the resistive switching properties of a solid electrolyte, usually a metal-oxide film, sandwiched in between two metal electrodes.[13−17] In the established literature, the switching mechanism is related to nanoionic processes of migration of oxygen species (valence change memory effect, VCM) or host metal ions from an electrochemically active electrode (electrochemical metallization memory effect, ECM), or both.[18] Despite the great efforts in investigating the switching mechanism, the role of extrinsic effects such as the surrounding environment in the memristive behavior still needs to be elucidated. Amorphous or polycrystalline films often have variable physicochemical properties such as structure, chemical composition, and stoichiometry, which can vary during switching operations These materials can dissolve and/or incorporate ions and/ or atoms and even clusters during operations, and a different distribution of active places/centers can be expected. From the technical point of view, the vertical device structure does not allow us to precisely define the highquality interface between oxide and moisture where the Received: July 19, 2020 Accepted: October 2, 2020 Published: October 14, 2020
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