Controllable multimodal switching in TaO <i>x</i> -based RRAM through Ar/O2 sputtering ratio and stacking sequence regulation

TaOx-based resistive random-access memory (RRAM) is a promising candidate for next-generation nonvolatile memory due to its high density, low power consumption, and simple architecture. This work investigates the influence of the Ar/O2 ratio and stacking configuration on the switching characteristics of TaOx RRAM devices. Thin films deposited at Ar/O2 ratios of 20:5 and 20:10 were used to fabricate Ta/TaOx/Ta2O5/ITO and Ta/Ta2O5/TaOx/ITO structures. By tuning the compliance current (Icc), the Ta/TaOx/Ta2O5/ITO device exhibits a transition from nonvolatile to volatile switching, while the Ta/Ta2O5/TaOx/ITO device transforms from digital to analog behavior. Both devices display multilevel resistance states at higher Icc and can emulate distinct synaptic functions at lower Icc. The Ar/O2 ratio and stacking sequence determine the distribution of oxygen vacancies, and Icc governs their migration, allowing multiple switching modes. Conduction mechanism analysis reveals that space charge-limited conduction dominates at high Icc, while Schottky emission becomes significant in the Ta/Ta2O5/TaOx/ITO device at low Icc. These findings clarify current-dependent switching mechanisms and provide structural design insights for high-performance and neuromorphic TaOx-based RRAM.