Photoelectron spectroscopic study on high-k dielectrics based nanoionics-type Re RAM structure under bias operation

We have demonstrated resistance switching using HfO₂ film with a Cu top electrode for nonvolatile memory applications, and revealed the Cu diffusion into the HfO₂ layer during the filament formation process. Resistive switching was clearly observed in the Cu/HfO₂/Pt structure by performing current-voltage measurements. The current step from a high resistive state to a low resistive state was of the order of 10³-10⁴ Ω, which provided a sufficient on/off ratio for use as a switching device. The filament formation process was investigated by employing hard x-ray photoelectron spectroscopy under bias operation. The application of a bias to the structure reduced the Cu₂O state at the interface and the intensity ratio of Cu 2p_3/2/Hf 3d_5/2, providing evidence of Cu₂O reduction and Cu diffusion into the HfO₂ layer. These results also provide evidence that the resistance switching of the Cu/HfO₂/Pt structure originates in a solid electrolyte (nanoionics model) containing Cu ions.