Introduction of WO₃ Layer in a Cu-Based Al₂O₃ Conductive Bridge RAM System for Robust Cycling and Large Memory Window

In this paper, we optimize a WO₃\Al₂O₃ bilayer serving as the electrolyte of a conductive bridge RAM device using a Cu-based supply layer. By introducing a WO₃ layer formed by thermal oxidation of a W plug, the hourglass shape of the conductive filament is desirably controlled, enabling excellent switching behavior. We demonstrate a clear improvement of the microstructure and density of the WO₃ layer by increasing the oxidation time and temperature, resulting in a strong increase of the high-resistance-state breakdown voltage. The high quality WO₃ microstructure allows thus the use of a larger reset pulse amplitude resulting both in larger memory window and failure-free write cycling.