Simulation of filament morphology in electrochemical metallisation cells

Electrochemical metallisation cells (ECM) are based on the principle of voltage-controlled formation or dissolution of a nanometre-thin metallic conductive filament between two electrodes separated by an insulating material, e.g. an oxide. The filament changes the resistance of the cell, allowing binary or even analogue memory states to be encoded. The lifetime of the filament depends on factors such as the materials and the voltage applied. Depending on the lifetime of the filament - from microseconds to years - ECM cells show promise for use in neuromorphic circuits, in-memory computing or as selectors and memory cells in storage applications. To enable these technologies with ECM cells, the lifetime of the filament must be controlled. Lifetime has often been associated with the morphology of the filament. Consequently, the parameters that determine the morphology of the filament are needed. In our work, we were able to show that both the applied electrical voltage and the mechanical stress within the insulating layer caused by the filament growth are decisive for the morphology of the filament. As expected, high voltage shows the formation of thin, directional filaments, whereas low voltage shows thick and solid filaments. What is special about our work is that we determine the morphology with a 2D continuum model, which has a much lower computational time than previous 2D Kinetic Monte Carlo (KMC) models. The main difference is that instead of looking at each atom individually, we calculate average currents. This represents an important step on the way to so-called 1D compact models with which complete circuits can be simulated.

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