Filamentary resistance switching is one category of switching mechanism that occurs in these materials, and the concept can be imagined to look something like a thunderstorm. The two typical materials showing this type of behaviour are TiO2 and NiO, where different shapes in conducting filaments and accordingly disparate switching behaviours have been reported.

There have been numerous studies on the phenomenological behaviour of these switching materials, but despite the progress that has been made, many issues remain unclear. For example, do the electrical conduction characteristics, type of carriers in the resistance switching material and type of electrodes used in the system have a significant influence on the switching even though the memory effect seems to be closely related with ionic motion?

Review article

To help summarize the status of the field, researchers from the Department of Materials Science and Engineering, Seoul National University, Republic of Korea, have studied the recent literature on filamentary resistance switching in several transition metal oxide materials, and were able to draw a consistent model.

According to the model, the filament is nucleated at the carrier injecting electrode and extends towards the opposite electrode. During this process, the filament shape can be either a conical column or a wire net depending on crystal chemistry and thermodynamic factors.

A clear understanding of the switching mechanism is important because this knowledge can provide the basis for solving several inherent disadvantages in filamentary resistance switching modules for memory device applications.

Performance boost

The team were able to identify an innovative way of significantly reducing switching time and energy consumption by a factor of ~1000 by tuning the switching sequence. By appropriately controlling the switching sequence, they could change the shape of the filaments and restrict the actual resistance switching to occur at a desirable location. The switching time was reduced to 120 ns from ~100 µs.

Full details can be found in the journal Nanotechnology.