Sub-1 nm Equivalent Oxide Thickness Al-HfO₂Trapping Layer with Excellent Thermal Stability and Retention for Nonvolatile Memory

Memory stacks for charge trapping cells have been produced exploiting Al-doped HfO2, Al2O3, and SiO2 made by atomic layer deposition. The fabricated stacks show superior stability and electrical characteristics, allowing for the engineering of sub-1 nm equivalent oxide thickness Al doped HfO2 trapping layer with excellent retention characteristics, also at high temperature. The low Al doping content (4.5%) used in this work leads to the HfO2 crystallization, upon thermal annealing, in the cubic/tetragonal phase with a dielectric constant value of 32. The trapping properties of the proposed stacks have been studied by means of physics-based models, highlighting the role of the different layers and the nature of the traps contributing to the charge storage in the memory stack.