Effect of the oxygen vacancy gradient in titanium dioxide on the switching direction of bipolar resistive memory

Resistive memory switching behavior depending on voltage sweep direction is studied by intentionally creating oxygen vacancies within titanium dioxide (TiO2). By inserting a reactive Ti layer on the TiO2, oxygen deficient TiO2−x layer is created, which then causes TiO2−x/TiO2 which has an oxygen vacancy gradient. This gradient of oxygen vacancy makes it possible to create an insulating TiO2 layer on the bottom electrode during the first reset with a negative bias at the top electrode. This insulating layer makes counterclockwise directional bipolar switching more stable. On the other hand, under the clockwise directional voltage sweeping, the first set switching is prevented by the insulating TiO2 layers created during the first and second reset, which leads to a short circuit due to local heating eventually.

► New resistive switching mechanism depending on voltage sweep direction in TiO2.
► An insulating TiO2 layer created during the first reset in the TiO2-x/TiO2 gradient made counterclockwise directional bipolar switching more stable.
► The first set switching was prevented by insulating TiO2 layers created during the first and second reset for the clockwise directional switching.