Ta Phase Engineering for Defect-Controlled Reliable Switching in Ultrathin TaO_x Memristors

Ultrathin TaO_x resistive random-access memory (RRAM) and related memristor devices require precise control of oxygen stoichiometry to achieve reliable switching at nanometer-scale thicknesses. Here, we demonstrate that the crystallographic phase of the Ta electrode critically governs defect formation and switching reliability in UV-ozone (UVO)-treated TaO_x devices. UVO oxidation of α-Ta forms a dense, near-stoichiometric switching layer with a controlled substoichiometric reservoir, whereas β-Ta leads to the formation of oxygen-deficient oxides with higher trap density. As a result, α-Ta-based devices exhibit significantly reduced device-to-device and cycle-to-cycle variability and improved endurance compared to β-Ta counterparts. Systematic structural, chemical, and electrical analyses reveal that phase-dependent defect distributions dictate filament evolution and switching stability. These findings establish electrode phase engineering as a key design parameter for achieving reliable ultrathin TaO_x memristors suitable for in-memory and neuromorphic computing applications.