Suboxide interface induced digital-to-analog switching transformation in all Ti-based memristor devices

Oxidation of TiN is a diffusion-limited process due to the high stability of the TiN metallic state at the TiN/TiO₂ junction. Hence, the TiN/TiO₂/TiN device being the inability to form a suitable interfacial layer results in the exhibition of abrupt current (conductance) rise and fall during the set (potentiation) and reset (depression) processes, respectively. Interfacial engineering by depositing Ti film served as the oxygen gettering material on top of the TiO₂ layer induces a spontaneous reaction to form a TiO_x interfacial layer (due to the low Gibbs free energy of suboxide formation). Such an interface layer acts as an oxygen reservoir that promotes gradual oxidation and reduction during the set and reset processes. Consequently, an excellent analog behavior having a 2-bit per cell and robust epoch training can be achieved. However, a thick interfacial layer may degrade the switching behavior of the device due to the high internal resistance. This work suggests that interfacial engineering could be considered in designing high-performance analog memristor devices.