Figure 4

Schematic illustration of switching mechanism using simple energy band diagrams with I - V characteristics. (a) Energy bands of pristine S1 structure device and ideal leakage current. For TiO₂, the solid line is due to the smaller energy gap of the defective TiO_x film. I-V of LRS and corresponding energy bands with conducting filaments for (b) S1 and (c) S2 devices. For TaO_x, the solid line is due to the lower energy gap caused by the presence of oxygen-deficient filament. The S1 devices show non-ohmic I-V due to TiO₂ layer formation at the W/TaO_x interface. (d) Filament oxidation and leakage current at HRS are shown for the W/TiO_x/TaO_x/W devices. Filament formation/rupture is controlled by the TiO₂ layer due to O²⁻ ion migration.