**3.2 Electrically induced redox reactions at the Interface**

The conducting oxide e.g. manganites or cobaltites based memristive devices that employ reactive metal electrodes practically show uniform electrical conduction throughout the active area of device [9, 21]. It is known that the electrical resistance in case of the fabricated devices is low and increases primarily as a function of the applied bias. Such positive bias is applied onto the top electrode of the fabricated device. A careful analysis employing the cross-sectional TEM along with EELS and HAXPES measurements revealed that the actual thickness of oxide layer formed at or near the interface enhances noticeably due to the electroforming treatment [14, 17]. In TiN/SiO2/FeOx/Fe device, Chang *et al.* demonstrated multilevel RS characteristics containing thin FeOx transition layer which essentially assist in achieving controlled current compliance in SET process and stopped voltage during RESET process. Interestingly, the controlled external electric conditions facilitate tunable resistive states. The distinct mechanism for multilevel RS behavior has been realized by distinguishing the electrical behaviors, statistically which indicated the mobile-ion-assisted electrochemical redox governed RESET process [22].
