Mechanisms of resistance switching in nanometric metal oxides and their dependence on electrodes

Resistance switching in HfO₂ metal-insulatormetal devices is investigated through current-voltage (I-V) and current-time (I-t) measurements. Depending on electrodes, a high-to-low resistance transition is observed in I-V characteristics at high or low voltages (OXRAM and CBRAM behaviors). This is correlated in the I-t characteristics to a progressive current increase, or to an abrupt current jump. Following the high-to-low resistance transition, several behaviors are observed: Non-switchable resistance (irreversible breakdown), evanescent low resistance state (spontaneous breakdown recovery), or fully switchable resistance (voltage-controlled reversible breakdown). The primary mechanism, common to both CBRAM and OXRAM devices, is hot electron injection at the cathode which leads to oxygen vacancies (defects) in the oxide bulk. Anode metal may diffuse along defect paths. In that case, the high-to-low resistance transition is due to the formation of metallic filaments across the oxide thickness (CBRAM case). When the anode metal diffusion is more difficult, the high-to-low resistance transition is ascribed to oxygen vacancy percolation paths (OXRAM case).