Recently, a research group from the Department of Materials Science and Engineering, Seoul National University, Republic of Korea, has reported an electronic resistance switching mechanism for a TiO2 film that is usually regarded as an ionic-type switching material. According to their study, the electronic resistance switching is induced by the non-uniform distribution of traps in the oxide and asymmetric potential barrier at interfaces.

When the traps are distributed non-uniformly, particularly when a much higher trap density is formed near one metal-insulator interface in a metal-insulator-metal structure, the barrier for trapping and detrapping becomes asymmetric with respect to the bias polarity. Figure (a) shows the schematic energy band structure considering the Coulombic interactions between the free carriers and trap centres (blue dot-dashed line) and the image force effect (red dashed line).

The team estimated the trap density and trap layer thickness and then discussed the change in switching behaviour when these values were changed. Figure (b) shows the difference in the asymmetric barrier height as a function of trap distance or trap density.

This study not only describes the electronic-type switching mechanism in detail, but also discusses the advantage of electronic-type resistance switching. The correlation between the ionic type unipolar resistance switching and electronic charge carrier driven resistance switching is also elucidated.

The researchers presented their results in a special issue of the journal Nanotechnology.