Impact of native defects and impurities in m−HfO₂ and β−Si₃N₄ on charge trapping memory devices: A first principle hybrid functional study

Abstract

Using hybrid density functional calculations, this paper systematically investigated the common defects in m‐HfO2 and β‐Si3N4 trapping layer, respectively, on the performance of charge trapping memory (CTM) devices. Defects may act as charge traps or fixed charges, however, only traps can be used to store charges. Thus, firstly, the paper distinguished traps or fixed charges of defects in trapping layer through the band alignment method. Then we can restrain the formation of defects that act as fixed charges in manufacturing CTM devices, which is very meaningful in improving the performance of CTM. Secondly, it studied the storage performance of traps in m‐HfO2 and β‐Si3N4 by analyzing the formation energy, the atomistic structural change during program/erase (P/E) cycles, and localization energy. The simulation results found that only some defects can be charge traps in m‐HfO2 and β‐Si3N4, and the charge transition of these traps only appeared between certain charged states. In addition, these traps show reversible structural change during P/E cycles and different localizing abilities for holes and electrons. Therefore, this study would provide some theoretical guidance for improving the performance of CTM.

Ab initio calculation of the evolution of [SiN4‐nOn] tetrahedron during β‐Si3N4(0001) surface oxidation

“…In addition, the lattice constant obtained by PBE optimization calculation ( a = 7.6044 Å, c = 2.9063 Å) is closer to the experimental value ( a = 7.608 Å, c = 2.9 Å) than the lattice constant calculated by the local‐density approximate (LDA) exchange‐correlation functional ( a = 7.569 Å, c = 2.890 Å). What's more, the PBE functional has also been adopted to deal with the structure of other inorganic nonmetallic materials besides Si 3 N 4 ‐based materials in the literature . The ultrasoft pseudopotential was selected to describe the interaction between valence electron and ion core.…”

“…What's more, the PBE functional has also been adopted to deal with the structure of other inorganic nonmetallic materials 30,31 besides Si 3 N 4 -based materials in the literature. 32 The ultrasoft pseudopotential was selected to describe the interaction between valence electron and ion core. The plane wave cut-off energy is 500 eV.…”

Research on c-HfO2 (0 0 1)/α-Al2O3 (1 -1 0 2) interface in CTM devices based on first principle theory

“…26 The calculated surface energies are listed in Table I, One basic rule of constructing hetero-interfaces is the higher stability and good matching of lattice parameters of two surface slabs. 45 Among various crystal planes of α-Al 2 O 3 , (0 0 0 1), (1 -1 0 2), and (1 1 -2 0) are the most stable surfaces.…”