HfO2/Al2O3 multilayer for RRAM arrays: a technique to improve tail-bit retention

In this work, the HfO2/Al2O3 multilayer structure is applied for RRAM arrays. Compared to HfO2 RRAM, the data retention failure of tail bits is suppressed significantly, especially for the high resistance state (HRS). The retention of tail bits is studied in detail by temperature simulation and crystallization analysis. We attribute the improvement of tail-bit retention to the decreased oxygen ion diffusivity caused by the Al2O3 layer. Furthermore, the HfO2/Al2O3 multilayer structure exhibits higher crystallization temperature, thus leading to fewer grain boundaries around the filament during the operations. With fewer grain boundaries, oxygen ion diffusion is suppressed, leading to fewer tail bits and better retention.