Bottom-electrode effect on switching behavior and interface reaction in nanoionic-based resistive changing memory

The bottom-electrode effect on a Cu/HfO₂ stack structure, which is an oxide-based resistive random access memory (ReRAM) structure, and the resistance switching behavior of the structures were investigated by hard X-ray photoelectron spectroscopy and by comparing the Pt and TiN bottom electrodes. In the Pt bottom electrode, a forward bias voltage induced the reduction of the unintentionally oxidized Cu top electrode and the Cu ion migration in the HfO₂ layer, resulting in the switching from the high resistivity to the low resistivity at approximately ±1 V. In contrast, the TiN bottom electrode induced the formation of oxygen vacancies in the HfO₂ layer and the thick Cu₂O layer at the Cu/HfO₂ interface, namely, it induced oxygen migration rather than Cu migration. The switching voltage of the Cu/HfO₂/TiN structure was twice that of the Cu/HfO₂/Pt structure. The switching mechanism in a nanoionic-type ReRAM structure can be controlled by changing the bottom electrode.