Understanding of switching phenomena in unipolar NiO-based RRAM

The electronic band structure of cation and anion vacancies in NiO is assessed using density functional theory in conjunction with the local density approximation and employing on site Coulomb corrections within the LDA+U method. The calculated formation energies identify the stability of charged vacancy states consistent with experimental reports. We propose a microscopic model for the formation and rupture of an electrically active filament in NiO targeted to explain the unipolar switching phenomenon observed in resistive change memory devices. The filament formation and rupture process are linked to the migration of oxygen in the oxide coupled to the oxidation/reduction of nickel atoms. The calculated migration barrier consistent with experimental activation barrier for retention can be used for making a retention model and evaluating the retention time.