Conduction mechanisms of filamentary resistive switching memristors based on nanoporous and nanotubular titania†

Abstract

Studying the electrophysical properties and conduction mechanisms of Au/TiO₂/Ti memristive structures based on nanoporous and nanotubular layers made of anodized titanium dioxide contributes to the improvement of quality indicators of prospective elements and nano-electronic devices derived from them. The paper measures the current–voltage characteristics and temperature dependencies of conductance in high-(HRS) and low-resistance states (LRS) for Au/TiO₂/Ti memristors with different thickness of nanoporous/nanotubular active layer. The importance of forming a nanotubular structure of the oxide layer with a thickness of 155–200 nm and an internal diameter of nanotubes of 21 ± 4 nm for improving the main characteristics of Au/TiO₂/Ti memristors when realizing the filamentary mechanism of resistive switching with the participation of oxygen vacancies is shown. The main parameters of electron transport, such as activation energy of electron conduction, electron mobility, dielectric relaxation time, and concentration of allowed states in the conduction band, are calculated for nanoporous and nanotubular TiO₂ layers in HRS using the framework of charge limited conduction mechanism. The parameters of the electron trap distribution are determined, such as concentration, capture cross-section, energy depth, distribution type, and characteristic temperature. It is shown that electron transport in LRS occurs by the Poole–Frenkel emission through filaments with metallic conduction type. Band diagrams are proposed to describe the conduction mechanisms involving oxygen vacancies for Au/TiO₂/Ti memristors in high- and low-resistance states.