Microscopic origins of electron trapping in amorphous silicon nitride (a-Si ₃ N ₄ ) and its role in charge-trap flash memory

Amorphous silicon nitride (a-Si 3 N 4 ) is widely used as the charge storage layer of charge-trap flash (CTF) memory devices, where its high density of deep localized electronic states enables long-term data retention at room temperature. Despite its technological relevance, the microscopic nature of the charge traps in a-Si 3 N 4 is still controversial. In recent years, atomistic modeling has enabled the characterization of structural and electronic properties of intrinsic defects in a-Si 3 N 4 . This review will discuss recent progress in atomistic modeling to elucidate the structural and electronic properties of intrinsic defects in a-SiN x . We demonstrate that a variety of structural irregularities, including over-and undercoordinated atoms, Si-Si bonds, vacancies and strained Si-N bonds, introduce localized electronic states in the amorphous network, which act as precursor sites for trapping and retaining electrons. The associated charge transition processes at these trapping sites are analyzed within the framework of nonradiative multiphonon theory and evaluated in the context of macroscopic CTF functionality. Additionally, we present a density functional theory (DFT)-based computational approach to estimate electron capture cross sections of intrinsic defect sites in a-Si 3 N 4 .