Uncovering the Indium Filament Revolution in Transparent Bipolar ITO/SiO_x/ITO Resistive Switching Memories

Transparent resistive switching random access memory (ReRAM) is of interest for the future integrated invisible circuitry. However, poor understanding of its working mechanism in transparent ReRAMs with the indium tin oxide (ITO) electrode is still a critical problem and will hinder its widespread applications. To reveal the actual working mechanism in transparent ReRAMs with the ITO electrode, we investigate the transparent ITO/SiO_x/ITO memory devices (∼82% transmittance in the visible region) and compare it with ITO/SiO_x/Au memory devices, which both can exhibit reproducible bipolar switching. The indium (In) filament evolution, which accounts for the bipolar switching behaviors in the ITO/SiO_x/ITO (or Au) memories, is directly observed using transmission electron microscopy on samples with different memory states (electroformed, ON, and OFF). These studies uncover the microscopic mechanism behind the bipolar switching in SiO_x-based ReRAM devices with the ITO electrode, providing a general guidance for the design of high-performance ReRAMs with large scalability and high endurance.