Fundamental mechanism behind volatile and non-volatile switching in metallic conducting bridge RAM

Abstract

We establish an active electrode (AE) selection criterion for volatile and non-volatile switching in metallic conducting bridge (CB) RAM, relevant to cross-point selector and memory applications. Using first principle calculations, we show that: (a) volatile versus non-volatile switching is determined by the energy difference A between the cluster configuration of the AE atoms in the high-resistance (HRS) state, and the filament configuration of the AE atoms in the low-resistance (LRS) state; volatile switching is achieved when A is large, whereas the system will exhibit non-volatile behavior when A ∼ 0; (b) the maximum LRS (ON-state) current, Imax that can be delivered while sustaining volatile (selector) operation is proportional to the magnitude of A for the AE. Using molecular dynamical (MD) + NEGF transport simulations, supported by experiments, we confirm the volatile (selector) switching characteristics of Ag/HfO2/Pt, and the non-volatile (memory) switching characteristics of Co/HfO2/Pt, as predicted by our criterion; the corresponding temporal characteristics are also evaluated. Finally, we calculate the expected switching characteristics for various active electrodes (AEs), showing excellent agreement with experimental results. Our findings enable the design of CBRAM-based selectors and memory with the required switching properties.