On the Bipolar and Unipolar Switching Mechanisms Observed in NiO Memory Cells Made by Thermal Oxidation of Ni

The NiO resistive-switching memory is under investigation due to its attractive properties and scaling potential. In this paper, we evidence the possible coexistence of both the bipolar and unipolar switching modes in NiO films. The bipolar mode can be activated provided the oxidation time is limited so that O^2- movement through easy paths allows electrochemical reduction/oxidation, while the unipolar mode is favored for longer oxidation times associated with larger NiO cell resistance. The memory states in bipolar and unipolar modes are shown to have different electrical properties.