Multiscale Investigation of Oxygen Vacancies in TiO₂ Anatase and Their Role in Memristor’s Behavior

Abstract

The structure, energetics, and transport properties of TiO2 anatase with different densities of oxygen vacancies are studied by computer simulations using a variety of techniques, ranging from first-principles to Monte Carlo methods, to span different time scales. This work is motivated by the recent development of memristive electronic devices, usually made of metal oxides in which arrays of defects control the resistance switching mechanism. Anatase, in particular, emerged as one of the most promising candidates for memristor design. However, the microscopic behavior of these multivacancy systems is not yet entirely understood. In this regard, electronic and transport properties of TiO2 anatase containing neutral and charged oxygen vacancies are investigated within density functional theory (DFT) by adding a Hubbard-like term to the generalized gradient approximation of the electron density (GGA+U). Calculated observables are the formation energy of oxygen defects, the cohesion energy of multivacancy systems, and the energy profiles of oxygen diffusion pathways, computed through the nudged-elastic band (NEB) approach. Furthermore, a kinetic Monte Carlo model (KMC) of the conductive channel formation in bulk anatase, based on the corresponding diffusion rates, is discussed. Finally, to demonstrate the relation between energetically stable structures and the conductive phase of memristors, we study electron transport within a tight-binding approximation to DFT, using the nonequilibrium Green’s function (NEGF) formalism.

Effect of Plasma-Enhanced Atomic Layer Deposition on Oxygen Overabundance and Its Influence on the Morphological, Optical, Structural, and Mechanical Properties of Al-Doped TiO2 Coating

“…Figure 3 presents a schematic representation that describes the mechanism responsible for an overabundance of oxygen on the surface of the films. Firstly, the oxygen ions from O 2 plasma imping distinct depth into the film [ 70 ] and through the physical diffusion mechanism [ 71 , 72 ] the oxygen reach the surface of the film being the oxygen consumed partially by Ti precursor. Finally, a new ALD cycle starts with the oxygen stored on the subsurface of the nanolaminates.…”

Towards synthetic neural networks: can artificial electrochemical neurons be coupled with artificial memristive synapses?

“…Further DFT-based investigations of structural and thermodynamic features of vacancies in various memristive systems were presented recently. [87][88][89][90] Phenomenological models, on the other side, are clearly sufficient for circuit-level simulations but are limited to specific switching mechanism(s) of the memristor and include various physical parameters that describe the active material characteristics in the device, thus reflecting potentially different switching mechanisms. We believe that a thorough understanding of atomic-scale processes leading to memristive behavior is fundamental in order to optimize material properties and help in the design of memory-based devices.…”

TiNF and Related Analogues of TiO2: A Combined Experimental and Theoretical Study

“…Our first-principles calculations are based on density functional theory as implemented in the Quantum ESPRESSO (QE) package. [24] We have used a local density approximation (LDA) to treat the exchange-correlation energy of electrons, and norm conserving pseudo potentials to represent the interaction between ionic cores and valence electrons. We employ an energy cut-off of 85 Ry to truncate the plane-wave basis set used in representation of Kohn-Sham wavefunctions.…”