Plasticity of parylene memristors: Compact phenomenological model and synaptic properties

Memristive devices have proven themselves as synaptic elements with rich internal dynamics and stochasticity for bio-inspired neuromorphic computing systems. Memristors based on parylene are of special interest due to their promising memristive properties, biocompatibility and ease of production. However, their synaptic behavior has not yet been fully demonstrated. In addition, the previously proposed model of resistive switching (RS) of these memristors was of a qualitative character and therefore important switching nuances turned out to be hidden. In this paper, a phenomenological model of resistive switching in parylene memristors is developed, based on the electromigration of metal cations from the top electrode, taking into account the stochastic nature of the RS process and conductivity of the parylene gap between the filament and the electrode, which determines various resistive states (plasticity) of the structures. The model is confirmed by a good correspondence between the calculated and measured current-voltage characteristics of the memristors. We also demonstrate various forms of bio-inspired plasticity of the structures, such as paired pulse facilitation/depression, long-term potentiation/depression and spike timing/amplitude/width/rate dependent plasticity. In the case of rate-based plasticity it resembles the theoretically and experimentally thoroughly studied BCM plasticity rule. The results obtained show the possibility of using such structures in the development of next-generation neuromorphic computing systems with promising calculating and learning capabilities.