Figure 2

Physical model for the observed 3-steps forming process.

(a) Typical 3-steps forming process observed in AZO/NiO/Pt structures under negative applied voltage. (b–f) Illustration of a physical model for the 3-stepsforming process: formation of a self-assembly ultra-thin O-rich AZO layer at the AZO/NiO interface and conducting filaments (CFs) in the NiO layer (1^st-step forming, b–d); formation of CFs in the self-assembly ultra-thin O-rich AZO layer (2^nd-step forming, e); irreversible breakdown in the NiO layer (3^rd-step forming, f).