Simulation Study of the Trapping Properties of HfO2-Based Charge-Trap Memory Cells

In this paper, the trapping properties of HfO2-based charge-trap cells have been extensively studied by means of a synergic use of material analysis, electrical characterization, and electrical and atomistic modeling. We assessed the impact of process conditions [i.e., postdeposition annealing (PDA)] on the material structure and the trapping behavior of the fabricated gate-stacks. Furthermore, we present reliable models for the HfO2 structure and for the defects responsible for the electron trapping. We found that HfO2 has a trap density comparable with that of SiN that depends on the PDA temperature. The HfO2 traps are shallower in energy than SiN traps, but retention of memory cells is still sufficient, also because of a slightly larger electron affinity and a larger permittivity than SiN that allows thicker layers while preserving the equivalent oxide thickness of the gate-stack.