Real-time study of imaging electron current density on metal filament evolution in SiO2 during in situ TEM

Conductive-bridging random access memory devices are a candidate for artificial synapses for neuromorphic computing. However, there is still an incomplete understanding of the fundamentals of the filament evolution process. In this work, we study the effect of three imaging electron current densities on nanoscale filament dynamics in a model Cu/SiO2/Cu structure during in situ TEM electroforming of the device. We find that the filaments grow from the anode to the cathode in the form of discontinuous precipitates for all the imaging electron current densities. However, increasing the imaging electron current density results in a larger injection of Cu into SiO2. Comparing the results of voltage ramp tests in air, in the TEM vacuum without electron irradiation and, in the TEM vacuum with electron irradiation, we suggest a possible mechanism of filament evolution in vacuum. Specifically, we postulate a vacancy defect generation enabled injection of Cu ions into the dielectric as the mechanism behind filament evolution in vacuum that reconciles differing observations found in the literature.