Improved Threshold Switching and Endurance Characteristics Using Controlled Atomic‐Scale Switching in a 0.5 nm Thick Stoichiometric HfO2Layer

Abstract

AbstractElectrochemical metallization cell–based threshold switching (TS) devices are promising candidates for selectors in high‐density cross‐point memory arrays. However, TS characteristics in density‐ and stoichiometry‐engineered solid electrolyte systems have not been studied. By adopting TS‐based stoichiometric and substoichiometric solid electrolyte HfO2layers, the localized atomic scale movement of Ag ions can be effectively controlled in ultrathin bilayers. The stoichiometric HfO2thickness is crucial to this. This study proposes defect‐ and density‐engineered bilayer TS with a 0.5 nm critical thickness of the stoichiometric HfO2layer, which maximizes various switching characteristics. The unstable filament in the ultrathin stoichiometric HfO2layer prevents the formation of stable Ag clusters owing to limited Ag injection into the dense and stoichiometric HfO2layer. In addition, the substoichiometric HfO1.91(1.5 nm) buffer layer prevents direct injection of Ag ions from the top electrode into the dense HfO2layer. These factors enable the bilayer design to achieve a high turn‐off speed of 100 ns, excellent endurance above 107cycles, low off current of ≈pA, and tightVthdistributions even for sub‐2 nm devices. These exceptional results demonstrate the possibility of designing density‐graded bilayer TS devices with high stability, fast switching, and high endurance.