Fig. 4.

Thin-film TiO_2 − x devices with controlled oxygen vacancy profiles are used to verify the switching mechanism. a Samples I and II contain reversed layer sequences of 15-nm TiO₂ and 15-nm TiO_2 − x (more vacancies) layers. These show opposite polarities of I-V curves in their virgin states. b. The switching polarities of these two samples are also opposite to each other. c. When more vacancies are introduced by adding a 5-nm Ti layer to the top interfaces of these two samples, the I-V curves change in totally different ways, confirming the dominant role of then non-ohmic interfaces in the thin-film devices [46]