Full-field Structural Microscopy of the Voltage-Induced Transition in VO₂ Neuromorphic Devices

Voltage induced phase transitions in VO₂ neuromorphic devices are one pathway to next generation neuromorphic computing. The archetypal correlated material, VO₂, has been forms conductive filaments under applied voltages leading to voltage-induced resistive switching accompanied by a structural phase transition. Local structural studies of the filament behavior are often limited due to time-consuming rastering which makes impractical many experiments aimed at investigating large spatial areas or temporal dynamics associated with the electrical triggering of the phase transition. Utilizing Dark Field X-ray Microscopy (DFXM), a novel full-field x-ray imaging technique, we study this filament formation process in-operando in VO₂ devices from a structural perspective. We show that prior to filament formation, there is a gain of the metallic rutile phase beneath the electrodes of the device. We observed that the filament formation follows a preferential path determined by structural nucleation sites within the device, which are predisposed to the phase transition and can become inclined to the rutile phase even after returning to room temperature.