Effect of the Oxygen Composition Control of HfO_x Films on Threshold and Memory Switching Characteristics for Hybrid Memory Applications

Abstract Considering a high‐density vertical X‐point memory array, the film thickness of an active device for the selector and memory needs to be scaled down. Here, the authors propose an AgTe/HfO_x‐based hybrid memory device with a film thickness of less than 10 nm by adopting a bilayer (HfO_1.8/HfO₂) film using precise composition control. Non‐volatile switching characteristics can be obtained by considering the formation of stable nanoscale Ag filaments in the nanoporous region in non‐stoichiometric HfO_1.8 deposited via sputtering. By contrast, volatile switching characteristics are achieved by an unstable atomic‐scale Ag path in stoichiometric HfO₂ deposited via plasma‐enhanced atomic layer deposition. Based on density functional theory calculations, it is confirmed that the stoichiometry of the HfO_x film is the key parameter that controls the switching characteristics. The bilayer (HfO_1.8/HfO₂) device exhibits excellent hybrid memory characteristics, such as distinct read margin (>1.5 V), high ON/OFF ratio (>10⁶), and extremely low OFF current (≈pA), for vertical X‐point memory applications.