Table 1.

The research status on switching mechanism of memristive devices

Properties	Common items for all types	Cation devices	Anion devices	Dual ionic devices
Chemical composition	Ion migration or phase change	Active metals, such as Ag, Cu Less active metals, such as Ti, Ta	Oxygen ions or vacancies Other anions, such as nitrogen vacancies	Both cation and anion
Driving force	Electric field Thermal effects (thermophoresis)20 Chemical potential gradient92	Nanobattery effect93 Interfacial energy minimization9	Relative role of field and temperature Thermodynamics2	Relative role of field and temperature Thermodynamics
Filament morphology	Filamentary Single and multiple filaments Dendrite-like filament45 Inverted or forward cone shape14	Chain of nanoparticles12 Inverted triangle crystalline13 Non-filamentary81	Non-filamentary94 Percolation path Filament rupture region	Percolation path Filament rupture region
Electron conduction mechanism	Ohmic conduction Schottky emission Tunneling (direct or FN)	SCLC model95 Quantum conductance96	P-F model, SCLC model97 Hopping (fixed-ranged, variable-ranged)98 TAT model	Trap Assisted Tunneling (TAT) model
Switching dynamics	Redox reaction Nucleation99 Microscopic picture of switching	Filament growth direction Growth dynamics14 Filament dissolution	Oxygen vacancy generation in the bulk Interstitial oxygen ion migration Dynamic motion of oxygen	Migration dynamics of cations and anions Reaction of cations and anions

Non-italicized indicates the conclusive findings, and italicized represents arguments not fully conclusive yet