Direct Observation of Conductive Filaments from 3d Views in Memristive Devices Based on 2d Sio2: Formation, Dissolution, and Vaporization

Abstract

Memristive devices, also known as memristors or ReRAMs, are promising candidates for next-generation memory. In classic electrochemical metallization (ECM) theory, there are only two states of conductive filaments: formation and dissolution. In our experiment, we found that the metallic filaments also vaporized leaving the observable defects in a series of memristive devices based on a Cu-doped 2D (two-dimensional) SiO2 electrolyte layer. Furthermore, the vapor from conductive filaments exfoliated the adjacent single layers of 2D SiO2. The morphologies of the conductive filaments in a memristive device (W/2D Cu doped SiO2/Ag) were studied using an SEM (scanning electron microscope) equipped with an FIB (focused ion beam) module. With the gradual removal of the electrolyte layer, cross-sectional images of conductive filaments were captured from perspective, top and side views. Based on these images, a three-dimensional model of the conductive filaments was proposed. All the findings suggested that the SET and RESET processes were complex where the formation, dissolution and vaporization of the conductive filaments occurred simultaneously. The vaporization of the conductive filaments permanently changed the surface morphology of the devices. This model, presented at the end of our paper, explains the irregular phenomena that occurred in I-V measurements.

Keywords: conductive filament, memristive device, Resistive switching, ReRAM；electrochemical metallization memory