Bias-Induced Interfacial Redox Reaction in Oxide-Based Resistive Random-Access Memory Structure

Abstract

In this chapter, we report on the investigation of the filament formation process in a resistive random-access memory (ReRAM) structure by performing hard X-ray photoelectron spectroscopy under bias operation. We demonstrated resistance switching for nonvolatile memory applications using a polycrystalline HfO2 film with a Cu top electrode, and revealed the diffusion of Cu 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-resistivity state to a low-resistivity state was on the order of 103--104 $Ω$, which provided a sufficient on/off ratio for use as a switching device. The application of a bias to the structure reduced the Cu2O at the interface and the intensity ratio of Cu 2p3/2/Hf 3d5/2, 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.