Photoelectron Spectroscopic Study on High-k Dielectrics Based Nanoionics-Type ReRAM Structure under Bias Operation

摘要

We have demonstrated resistance switching using HfO_2 film with a Cu top electrode for nonvolatile memory applications, and revealed the Cu diffusion into the HfO_2 layer during the filament formation process. Resistive switching was clearly observed in the Cu/HfO_2/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 10~3-10~4 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 Cu_2O state at the interface and the intensity ratio of Cu 2p_(3/2)/Hf 3d_(5/2), providing evidence of Cu_2O reduction and Cu diffusion into the HfO_2 layer. These results also provide evidence that the resistance switching of the Cu/HfO_2/Pt structure originates in a solid electrolyte (nanoionics model) containing Cu ions.