Ab initio study of oxygen vacancy filament formation at Ta/HfO2 interface

The resistive switching (RS) behavior of resistive random access memory (RRAM) based on oxygen vacancy (VO) conduction is significantly affected by the interface properties between metal electrode and oxide layer, yet the modulation between the RS behavior and the physico-chemical properties of the interface is still not very clear. In this study, the correlative role of Ta/HfO2 interface with the RS behavior in HfO2-based RRAM is explored at atomic level. First-principles thermodynamic calculations show that the strong interaction between three-fold oxygen vacancies (VO3) leads to a formation of VO3-based conductive filament (CF) along direction perpendicular to the interface. Four-fold oxygen vacancies (VO4) make a major contribution to the re-formation and growth of CFs during the set process by diffusing into the residual filaments. The results of electronic properties further indicate that as the number of VOs perpendicular to the interface increases, the charge redistribution between O and Ta atoms at the interface is significantly increased, and more electron clouds are gathered around VOs. This is the underlying mechanism of forming a conductive channel. This study reveals the important regulation mechanism of the interface characteristics between metal electrode and oxide layer in RRAM on the formation and growth of VO-based CFs.