Effects of heterogeneities on the voltage-induced filament formation in VO₂-based neuromorphic devices

VO₂ is a key material for the construction of memresitive devices with neuromorphic function due to its electrically induced resistive switching and conductive filament formation. In this work we provide numerical simulations and structural analysis of the filament formation in VO₂ devices in support of recent dark-field X-ray microscopy (DFXM) measurements, which is a novel full-field X-ray imaging technique that captures the filament formation process operando. We use the Mott resistor network (MRN) model to mesoscopically describe the VO₂ sample as a two-dimensional grid of resistors such that each one’s resistance depends on the local temperature via a Landau free energy functional. Our simulations demonstrate that the rutile metallic filaments of the VO₂ sample can contain isolated monoclinic clusters, in agreement with the experimental DFXM data and indicating structural non-uniformity within the conducting filament. Additionally, we reproduce recent experimental findings that indicate a new medium-term memory mechanism in VO₂ mediated by sites that tend to switch at significantly lower voltages after electrical cycling, a tendency that persists through brief cooling. These numerical simulations and experimental observations provide insight into the subtle structural features of the filamentary channel and surrounding regions during voltage cycling in VO₂-based devices.