Transition of metallic and insulating Ti sub-oxides in bipolar resistive switching TiO x /TiO y frameworks due to oxygen vacancy drifts

Bilayer TiO _x (oxygen rich, region 1)/TiO _y (oxygen poor, region 2) homojunctions were evaluated as resistive switching elements where the TiO _x layers were designed with various oxygen contents. Depending on the oxygen ion content, controllable memory windows were observed by changing the off-state (high-resistance state), while the on-state (low resistance) was left with very little change. The cause of the variable memory windows in resistive switching phenomena appears to be the increasing amounts of movable oxygen ions between the TiO _x and TiO _y layers. In addition, the X-ray photoelectron spectroscopy measurements of the initial, low resistance, and high-resistance states in the homojunctions demonstrated the possible change of metallic and insulating Ti sub-oxide phases at the interfaces and oxygen ion rich region due to the migration of oxygen ions.