Microscopic understanding of the low resistance state retention in HfO2 and HfAlO based RRAM

We study in detail the impact of alloying HfO₂ with Al (Hf_1-xAl_2xO_2+x) on the device characteristics through materials characterization, electrical measurements and atomistic simulation. Indeed, movements of individual oxygen atoms inside the dielectric are at the heart of RRAM operations. Therefore, we performed diffusion barrier calculations relative to the oxygen vacancy (VO) movement involved in R_on data retention. Calculations are performed at the best level using ab initio techniques. Our study provides an insight on the improved R_on stability of Hf_1-xAl_2xO_2+x RRAM, via a simple explanation based on its higher atomic density (atoms/cm³) associated with shorter bond lengths between cations and anions in the presence of Al.