Retention Model of TaO/HfO _x and TaO/AlO _x RRAM with Self-Rectifying Switch Characteristics

A retention behavior model for self-rectifying TaO/HfO _x - and TaO/AlO _x -based resistive random-access memory (RRAM) is proposed. Trapping-type RRAM can have a high resistance state (HRS) and a low resistance state (LRS); the degradation in a LRS is usually more severe than that in a HRS, because the LRS during the SET process is limited by the internal resistor layer. However, if TaO/AlO _x elements are stacked in layers, the LRS retention can be improved. The LRS retention time estimated by extrapolation method is more than 5 years at room temperature. Both TaO/HfO _x - and TaO/AlO _x -based RRAM structures have the same capping layer of TaO, and the activation energy levels of both types of structures are 0.38 eV. Moreover, the additional AlO _x switching layer of a TaO/AlO _x structure creates a higher O diffusion barrier that can substantially enhance retention, and the TaO/AlO _x structure also shows a quite stable LRS under biased conditions.