Unveiling the Resistive Switching Mechanism and Low Current Dynamics of Ru-based Hybrid Synaptic Memristors

Mobile Ru ions in oxide media have been reported as a novel species that offer extremely low switching currents for memristors. However, their bi-stable resistive-switching (RS) and low-switching currents dynamics have not been quantitatively unveiled. Here, the bi-stable RS mechanism via in-depth field-induced atomic migration and chemical bonding state studies is elucidated, showing that the RS of the Ru-based hybrid memristor (RHM) is possible via the simultaneously controlled hybrid Ru cation and oxygen anion. Additionally, the Ru ion mobility is quantitatively obtained via atomic moving distance and switching time measurements, demonstrating that the lower Ru ion mobility, compared to other conventional mobile species in oxide media, can be the origin of the low-switching currents. It is found that the current conduction mechanism of the low-resistance-state in RHMs has temperature-range-dependencies. The direct tunneling conduction mechanism is dominant in relatively low temperatures; however, the ionic transport and thermally activated hopping conduction mechanism govern the current flow in high temperatures. Owing to the low Ru ion mobility, the RHM exhibits highly linear synaptic plasticity with a low-conductance regime, showing outstanding energy efficiency compared to other memristors in image recognition tasks. These findings can contribute to improving the feasibility of hyper-scale synaptic cores consisting of RHMs. The bi-stable resistive switching mechanism and ultra-low-current dynamics of the Ru-based hybrid memristors, which utilize the synergistic effects of valence-change memory and electrochemical-metallization cells, are elucidated by in-depth studies. It is found that the current conduction mechanism of the low-resistance state in the Ru-based hybrid memristors has temperature-range dependencies; various conduction mechanisms governed the current flow by hybrid resistive switching dynamics. image