Universal Synaptic Plasticity of Interface-Based Second-Order Memristors

Abstract

Second-order memristors with their internal short-term dynamics display behavioral similarities with biological neurons and constitute an ideal basis unit for hardware neuromorphic networks, aims at treating spatio-temporal tasks. Here, La_0.7Sr_0.3MnO₃/BaTiO₃/La_0.7Sr_0.3MnO₃ second-order memristive devices are investigated whose resistances and temperature dependencies range, on the same chip, from semiconductor to metal, but exhibit a universal neuromorphic plasticity. All devices may be described using a compact phenomenological model of current conduction, showing that resistive switching originates from interfaces, through charge trapping. Remarkably, the processes of short-term memory gain/loss and long-term consolidation/forgetting are the same whatever the device type. Only the synaptic transmission weights and the excitation/relaxation times with respect to stimuli differ, as it occurs for synapses/neurons in the brain. The weights may be tuned by the sole use of the frequency of stimuli (the activity rate), their evolution being dependent on previous activities (the history). Metal and semiconductor devices display the same in-operando dynamics of potentiation or of depression, the transition from one regime to another being history-dependent. The threshold frequencies are slightly lower in semiconducting devices. This work contributes to better understanding of memristive switching and plasticity and is relevant for the development of brain-mimetic neural networks with new programming paradigms.