Impact of Oxygen Vacancy Ordering on the Formation of a Conductive Filament in TiO₂ for Resistive Switching Memory

The electronic properties of rutile TiO 2 with an ordered arrangement of oxygen vacancies show a transition from a resistive to conductive oxide as a function of vacancy ordering. Vacancy ordering along two different directions [110] and [001], studied by the density functional theory, predicts that the geometries in which the vacancy-to-vacancy interaction is the strongest, within the nearest neighbor coordination, are thermodynamically favorable and of technological importance. The oxygen vacancies induce several occupied defect states of Ti 3 d character, and according to our model, the vacancies are the mediators of electron conduction, while the conductive filament is formed by Ti ions. We propose that the formation of these types of conductive filament is intrinsically connected to the observed defect-assisted tunneling processes and oxide breakdown issues.