Fig. 5
From: Multi-level resistive switching in hafnium-oxide-based devices for neuromorphic computing
Illustrations of different proposed approaches to explain or control switching mechanisms. Such schematics should be avoided without detailed underlying understanding. Gray at the top and bottom indicate electrodes, pale yellow is the switching layer, plussed squares indicate oxygen vacancies. a In many publications, an oxygen-vacancy-rich layer (shaded red), either by oxygen scavenging from an electrode or a dedicated oxide layer (e.g., TiOx), is used to enhance switching properties. However, there are different explanations as to the shape of the filament and its change during filamentary switching. b In [43], Pt nanoparticles embedded in the switching layer were used to enhance the electric field and guide the formation of filaments. c In [44], nanoindentations in the top electrode enhanced the electric field underneath the indentation to guide the formation of filaments. d In [96], vertically aligned nanocomposite films of two different materials (HfOx and CeOx) were used to guide filament formation along the resulting grain boundaries. e In [36], in a hybrid approach, vertically oriented phase separation in amorphous films was used to form effective top electrodes and restrict the switching process to the interface region (shaded green). f In [39], a RS element was integrated on top of a MOSFET gate contact, and the voltage division due to the RS caused large effective threshold voltage shifts and thus different source-drain currents