Microscopic mechanisms of filament growth in memristor

Abstract

The growth of a filament in an oxide medium with top electrode of Ag and bottom electrode of Pt is analyzed by considering the microscopic processes. The filament, either made up of Ag metal ions or oxygen vacancies, is considered to nucleate at the interface and grow under the influence of the applied electric field and injection of the defects from the interface. The flux of current is used to calculate the joule heating and the resulting temperature change in the filament after solving the thermal diffusion equation. In addition, the concentration of defects in the filament is evaluated from the equilibrium concentration and the loss of defects from the filament using the analytical solution to the mass diffusion equation. The rise in temperature, the concentration of defects, electrical current carried, and the height and radius of the filament are determined for several increments in time. The results showed that the growth of the filament is a complex process dependent on the several interdependent parameters. The important parameters are the initial concentration of defects, the applied voltage, activation energy for atomic jumps, free energy of formation of defects and the activation energy for diffusion. The numerical results are presented for ZnO with Ag top electrode and Pt bottom electrode by considering different choices of the parameters to illustrate their relative importance.