Bipolar switching properties of amorphous TiO2 thin film grown on TiN/Si substrate

Pt/TiO2/TiN device with the amorphous TiO2 film grown at room temperature under an oxygen partial pressure of 1.0 mTorr showed reliable bipolar switching behavior. During the electroforming process, a large number of oxygen vacancies formed in the TiO2 film and accumulated at the Pt/TiO2 interface. The barrier height of the Schottky contact of the Pt/TiO2 interface was reduced owing to the presence of these oxygen vacancies, resulting in the low-resistance state (LRS). Moreover, oxygen ions diffused into the TiN electrode during the electroforming and set processes. On the other hand, the oxygen ions in the TiN electrode diffused out and reacted with oxygen vacancies in the TiO2 film during the reset process, and the device changed from the LRS to the high-resistance state (HRS). Conduction in the LRS and HRS can be attributed to Ohmic conduction and the trap controlled space charged limited mechanism, respectively.