TiO₂—a prototypical memristive material

Abstract

Redox-based memristive switching has been observed in many binary transition metal oxides and related compounds. Since, on the one hand, many recent reports utilize TiO(2) for their studies of the memristive phenomenon and, on the other hand, there is a long history of the electronic structure and the crystallographic structure of TiO(2) under the impact of reduction and oxidation processes, we selected this material as a prototypical material to provide deeper insight into the mechanisms behind memristive switching. In part I, we briefly outline the results of the historical and recent studies of electroforming and resistive switching of TiO(2)-based cells. We describe the (tiny) stoichiometrical range for TiO(2 - x) as a homogeneous compound, the aggregation of point defects (oxygen vacancies) into extended defects, and the formation of the various Magnéli phases. Furthermore, we discuss the driving forces for these solid-state reactions from the thermodynamical point of view. In part II, we provide new experimental details about the hierarchical transformation of TiO(2) single crystals into Magnéli phases, and vice versa, under the influence of chemical, electrical and thermal gradients, on the basis of the macroscopic and nanoscopic measurements. Those include thermogravimetry, high-temperature x-ray diffraction (XRD), high-temperature conductivity measurements, as well as low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and LC-AFM (atomic force microscope equipped with a conducting tip) studies. Conclusions are drawn concerning the relevant parameters that need to be controlled in order to tailor the memristive properties.

Role and Optimization of the Active Oxide Layer in TiO2‐Based RRAM

“…[ 17 ] TiO 2 based junction devices were one of the fi rst semiconductor devices to be identifi ed as memristors and have been studied extensively. [18][19][20] The study of such devices has now reached the state of device behavior optimization. A range of factors have been identifi ed which directly infl uence the device performance and reliability, including annealing.…”

TinO2n−1Magnéli phases studied using density functional theory

“…This in turn can be changed (write operation) and measured (read) when subjected to an electric field. The insulator layer is a nanometer-thick thin film, which can be composed of a wide variety of materials, such as binary oxides [8], perovskites [9][10][11][12], as well as many other compounds, which are known for their resistance switching properties [13,14].…”

Probing the oxygen vacancy distribution in resistive switching Fe-SrTiO3 metal-insulator-metal-structures by micro-x ray absorption near-edge structure

“…1,2 The key role of oxygen nonstoichiometry and oxygen-deficient oxide-phases as the underlying mechanism of the resistance change has been recognized for many different oxide systems (e.g., TiO 2 , 3,4 Ta 2 O 5 , 5 SrTiO 3 . 6 It is becoming widely accepted that the resistance switching process in SrTiO 3 is related to the movement of oxygen vacancies and the associated electron doping.…”