Theoretical insights and experimental characterization of $$\hbox {HfO}_2$$ HfO 2 -based OxRRAMs operation

Abstract

The intensive research in resistive random access memories (RRAM) field has brought in significant improvements in the performance, optimization and reliability of the devices as well as more understanding on their operation. This was made possible through the combination of different tools starting from material engineering to device characterization, modeling and simulations. In this review, we bring an overview of our recent work on RRAM through experimental characterization and first-principles calculations. We explore the effects of metal electrodes on the switching performance and conductive filament (CF) stability of $$\hbox {HfO}_2$$ oxide-based RRAM (OxRRAM). With the insight gained from the experimental data, we employ first-principles calculations to have a better microscopic understanding on OxRRAM operation. We show that CF stability and device operating voltages strongly depend on the electrode material. Ti being an electrode material of high interest, we investigate the type of $$\hbox {Ti/HfO}_2$$ interface that may be formed and propose a probable composition. We also study the formation and migration of extended Frenkel-pair (EFP) defect in $$\hbox {HfO}_2$$ which we consider to be the prototype defect responsible for OxRRAM degradation leading to CF formation. This EFP emission occurs through a cascading migration of O atoms inside $$\hbox {HfO}_2$$ lattice. Based on EFP formation and diffusion, we present a simplified CF formation model. Finally, we study low resistance data retention failure in OxRRAM through $$\hbox {HfO}_2$$ , $$\hbox {Hf}_{1x}\hbox {Al}_{2x}\hbox {O}_{2+x}$$ (HfAlO) and $$\hbox {Hf}_{1-x}\hbox {Ti}_{x}\hbox {O}_{2}$$ (HfTiO) type of cells. We link its origin to the lateral diffusion of oxygen vacancies at the constriction/tip of the conductive filament in $$\hbox {HfO}_2$$ -based RRAM.