Stress Induced Vacancy Clustering Mechanism of Resistive Switching in Hafnium Oxides

Reversible changes in the conductivity of HfO₂ dielectric film between high and low resistive states of a metal-insulator-metal memory cell were attributed to the formation of oxygen vacancies and their clustering across the insulator layer. In this study we present an innovative model which includes generation of two-charged states of oxygen vacancies at the anode, their diffusion to the cathode, transformation to one-charged state, and then to neutral vacancies. Vacancy clusters in the insulator layer are built from only neutral vacancies, while the kinetics of the clustering process is controlled by diffusion of mobile one-charged state vacancies. Resistive switching is treated as the formation of critical size vacancy cluster which provides continuous conductive path through the dielectric layer. Good agreement between the experimental data and the theoretical bias and temperature dependences for the delay time was obtained.