Control of electrochemical reduction behavior in nonequilibrium Al-doped TiO2 thin films

To develop resistive switches using TiO2, the control of their switching voltage is a crucial issue. This study shows how acceptor and compensating oxygen vacancies modify the resistive switching behavior from both the experimental and theoretical points of view. Nonequilibrium TiO2 thin films doped with acceptor Al with oxygen vacancies were prepared by pulsed laser deposition. Al doping results in a clear reduction in the switching voltage when the TiO2 thin films are operated as a unipolar-type switch but not when they are operated as bipolar-type switches. Density functional theory calculations revealed that the doped Al and compensating oxygen vacancies ( [ A l ′ Ti ] = 2 [ V O ⋅ ⋅ ] ) promote the formation of oxygen vacancies compensated by electrons ( 2 [ V O ⋅ ⋅ ] = n ) due to the defects association of 2 A l ′ Ti − 2 V O ⋅ ⋅ − 2 e ′. This defect cluster functions like the formation center of conductive nanofilaments for the electrochemical reduction. It was concluded that by promoting the formation of oxygen vacancies compensated by electrons, Al doping results in a decrease in energy consumption of the unipolar-type resistive switching.