Visualizing CBRAM Filaments: CBRAM (conductive bridging RAM) is a promising non-volatile memory technology offering low-power operation, fast switching, high endurance and scalability. CBRAM’s redox (reduction-oxidation)-based electrochemistry relies on the fact that some amorphous materials with relatively large amounts of metal can behave as solid electrolytes. Under a voltage bias, metal ions in such an insulating amorphous layer can be reduced to form a conductive filament, or pathway, through it. The process can be reversed as needed, thereby enabling the reading and writing of memory data. Device performance is directly related to the properties of the conductive filament, but because the filament is internal to the solid layer, it is difficult to see, which makes it difficult to optimize. IMEC researchers will describe a 3D imaging approach that enables them to “see” how and where the filament forms in the amorphous layer. Similar to medical CAT scans which take multiple X-ray “slices” of internal organs and combine them to create 3D images, the IMEC approach uses conductive atomic force microscopy to take many slices of the amorphous layer. Each slice maps where electrical conduction is occurring, and the slices are then combined to render 3D images of the entire conductive filament.
The left image is a model of the slices, with blue showing the area of conduction in each slice. The middle image is a model with the slices combined to show the filament. The right image shows measurements of the conductive filament superimposed onto the computer model of it.
(Paper #21.6, “Conductive-AFM Tomography for 3D Filament Observation in Resistive Switching Devices,” U/ Celano et al, IMEC)