We report an approach to design a metal-insulator-metal (MIM) structure exhibiting multilevel resistive switching. Toward this end, two oxide layers (TiO₂ and Al₂O₃) were combined to form a bilayer structure. MIM structures demonstrate stable bipolar switching relative to the resistive state determined by the bias voltage. The resistive state of such bilayer structures can be electrically tuned over seven orders of magnitude. The resistance is determined by the concentration of oxygen vacancies in the active layer of Al₂O₃. To elucidate a possible mechanism for resistive switching, structural studies and measurements have been made in the temperature range 50–295 K. Resistive switching occurs over the entire temperature range, which assumes the electronic character of the process in the Al₂O₃ layer. The experimental results indicate that hopping transport with variable-length jumps is the most probable transport mechanism in these MIM structures.

In this paper, we report a model that interprets the mechanism of bipolar resistive switching in thin metal oxide layers as a purely electronic process. Based on the experimental results, we find that the main transport mechanism in our compensated highly resistive semiconductor is related to space-charge-limited current traps. The S-shaped I–V characteristics of the structure layers of Pt/PbO/Pt with stable bipolar resistive switching demonstrate filamentary charge carrier injection in the bulk of the film. This leads to the formation of conductive filamentary areas in the metal-oxide film. We associate the transition from the high resistive state to the low resistive state (SET process) with the trap-filling limit being reached in the local conductive filamentary area, accompanied by the transition of this area to a state with a high degree of degeneracy. The stability of the conductive filament is provided by the potential barrier formed on the border with the main volume of the lead oxide compensated semiconductor film. The return to the initial state (RESET process) occurs at the injection of opposite charge carriers into the degenerate semiconductor in the local filamentary area, followed by the charge carrier recombination and transformation of this area into a highly resistive compensated semiconductor.