Disproportionation and comproportionation reactions of resistive switching in polycrystalline NiOx films

The NiO$_{x}$ thin film exhibit excellent bistable unipolar resistive switching, which has strong potential in nanoscale nonvolatile-memory applications. The underlying mechanism of NiOx resistive switching is still in debate. We studied the chemical bonding states of Ni 2p and O 1s at high/low resistance spots by focused X-ray photoemission spectroscopy. The disproportionation and comproportionation reactions of 3NiO $\leftrightarrow $ Ni + Ni$_{2}$O$_{3}$, accounts for the resistive switching of NiO$_{x}$. The calculated Gibbs energy of the reaction indicates the reversibility of the reaction thermochemically. The dynamic breathing of the filaments with switching was observed by conducting atomic force microscopy.