Oxygen Exchange Processes between Oxide Memristive Devices and Water Molecules

Abstract

Resistive switching based on transition metal oxide memristive devices is suspected to be caused by the electric-field-driven motion and internal redistribution of oxygen vacancies. Deriving the detailed mechanistic picture of the switching process is complicated, however, by the frequently observed influence of the surrounding atmosphere. Specifically, the presence or absence of water vapor in the atmosphere has a strong impact on the switching properties, but the redox reactions between water and the active layer have yet to be clarified. To investigate the role of oxygen and water species during resistive switching in greater detail, isotope labeling experiments in a N /H O tracer gas atmosphere combined with time-of-flight secondary-ion mass spectrometry are used. It is explicitly demonstrated that during the RESET operation in resistive switching SrTiO -based memristive devices, oxygen is incorporated directly from water molecules or oxygen molecules into the active layer. In humid atmospheres, the reaction pathway via water molecules predominates. These findings clearly resolve the role of humidity as both oxidizing agent and source of protonic defects during the RESET operation.

Recent Developments and Perspectives for Memristive Devices Based on Metal Oxide Nanowires

“…For example, electrical measurements in different atmospheres allowed to unveil the n-type conductive path responsible resistive switching in MgO core-TiO 2 shell nanowires. [200][201][202][203] Using a completely different approach, resistive switching was observed also considering conductive nanowires covered by an oxidized shell layer, in which the switching occurs along the radial direction of the NW. It is important to remark that this strategy can be adopted only in planar devices and not in widely studied capacitor-like devices where the switching mechanism is hidden in stacked sandwich structures: for these reasons, nanowires can be considered a good platform to investigate the resistive switching mechanism in a wide range of materials.…”

Investigation of the Eightwise Switching Mechanism and Its Suppression in SrTiO3 Modulated by Humidity and Interchanged Top and Bottom Platinum and LaNiO3 Electrode Contacts

“…Rectification is characteristic of a Schottky diode, which is governed by the metal contact with the higher work function being in our case Pt. [16,18] Also initial studies by Messerschmitt et al show that the maximum current during the set process drops with humidity. This direction emerges only after lowering the humidity level to 5% RH where a current decrease at positive applied bias of about five orders of magnitude is observed.…”

“…[10] Changes of resistance states in the oxides are facilitated by ion transport under high local electrical fields. [1] Recently however, it has been shown that also the change in the relative humidity in the surrounding atmosphere will change the resistive switching behavior of TaO x , [13,14] HfO x , [13] SrTiO 3 , [15,16] and TiO 2 . [11] In general oxidebased memristive devices work on the principle of nonvolatile resistance change upon the application of an electrical potential.…”

“…Using H 2 18 O exchange experiments on SrTiO 3 Heisig et al recently confirmed that oxygen incorporation from humidity happens at room temperature with the driving force of high electric fields rather than Joule heating in the switching oxide. [16] The incorporation through filling of oxygen vacancies can be defined using Kröger-Vink notation [13] …”

Memory materials and devices: From concept to application

“…The ions participating in the RS are anions, typically oxygen ions (or oxygen vacancies). Other than ECM cells, where the sources of cations are primarily the active electrode or nanoparticles in the switching layer matrix, oxygen ions in VCM cells are mainly from the external atmosphere, such as oxygen and water molecules, and the switching layer matrix. Without the oxygen‐containing atmosphere, for example, in pure N 2 , stable RS can hardly occur .…”