Linear Potentiation in Filamentary Valence Change Mechanism With Sub-100 ps Pulses

Redox-based resistive random access memory (ReRAM) has emerged as a promising technology for next-generation non-volatile memory and neuromorphic computing applications. Among the various ReRAM types, valence change mechanism (VCM) based devices have gained significant attention due to their fast switching, low energy consumption, good scalability, high endurance, and multilevel capability. However, for synaptic applications, gradual and linear conductance changes are required to mimic biological learning. Unfortunately, the typically abrupt SET switching in filamentary VCM makes this difficult, which is a key challenge for neuromorphic systems. In this study, we investigated the SET switching kinetics of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {Pt/TaO_{x}/Ta/Pt} $ </tex-math></inline-formula> stack devices in response to repeated sub-100ps pulses, and observed a transition from abrupt to gradual, linear switching behavior. Our findings demonstrated that the pulse width and amplitude were crucial in facilitating this transition, with 50ps pulses enabling a linear conductance change (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2} = 99.5\,\%$ </tex-math></inline-formula>) over 100 pulses in the linear region. Although variability remains a key challenge, the initial low conductive state (LCS) is expected to influence the switching dynamics, with previous reports suggesting that a low LCS typically leads to more abrupt switching. However, our findings reveal that the use of short pulses mitigates this effect, thereby allowing linear transitions even when starting from a low initial LCS.