Multi-Scale Modeling of Charge Dynamics in a Neuromorphic Device Based on PEDOT:PSS

A first principle multi-scale model is used to study the charge dynamics of a neuromorphic device based on PEDOT:PSS in an NaCl electrolyte system. We compare the results with and without the application of an orthogonal electric field to study the device operation properties. The first step of the model is the classical molecular dynamics (MD) simulation of the device whose atomistic morphology is then partitioned into hopping sites, for which energies are calculated by a QM/MM method.<br/>The coordinates of the sites are used to construct a list of molecule pairs, for which reorganization energies, electronic coupling elements and eventually the Marcus hopping rate are calculated.<br/>A directed graph is defined from the neighbor list and hopping rates where kinetic Monte Carlo (KMC) and graph theory are used to analyze the charge dynamics.<br/>Our results reveal a different energy landscape when an external electric field is applied orthogonal to the device. Also, both the distribution of coupling elements and site energy correlation functions are altered by the electric field. Accordingly, KMC results show that when the electric field drives the Na+ ions out of the device channel, charge dynamics are faster and have a large flow order parameter.<br/>Random walk theory is used for studying the resistance/conductance for this neuromorphic charge network, and percolation is simulated numerically to reveal its connectivity. Electric field-sensitive regions are identified by the distribution of site voltages and Ricci curvature in the graph, which is related to the fast/slow dynamics from the KMC simulations. Our study reveals the linkage between the elementary process on atomistic/electronic level and the device performance.