Variability Reduction with Bilayer RRAM Device

The inherent stochastic behavior of filamentary switching introduces significant cycle-to-cycle (C2C) fluctuations in the device characteristics, which poses a challenge to the practical applications of resistive random-access memories (RRAMs). Here, we report a simple bilayer oxide-based device structure of $\mathbf{TaO}_{\mathbf{x}}$ /HfO2 on a 180-nm CMOS substrate to address this variability issue and improve the overall performance of the memory device. The improved switching variability in the bilayer stack is attributed to the incorporation of a conductive $\mathbf{TaO}_{\mathbf{x}}$ thin film, which serves as the switching layer after the conductive filament formation in HfO2. More specifically, the switching happens at the interface between the conductive filament and $\mathbf{TaO}_{\mathbf{x}}$ and exhibits a more gradual and less stochastic behavior than filamentary switching. As a result, 3-bit multi-level non-overlapping switching can be demonstrated in $\mathbf{TaO}_{\mathbf{x}}$ /HfO2 bilayer RRAM devices. These findings could be crucial for the high density data storage applications of RRAMs.