Reliable charge storage in dielectric materials enabled recent three dimensionally integrated flash memory devices. Currently known dielectric stack based on silicon nitride charge storage layer may challenge further dimensional and voltage scalings. The definite electrostatic requirement of dielectric material parameters for a further scaling is the enhancement of dielectric constant values. However, hundreds of suggestions based on higher dielectric constant materials for memory application have been failed in commercialization. In this talk, it will be shown that the dielectric thin film for charge storge should have amorphous phase to exhibit nonvolatile charge storge characteristics. Furthermore, a further design in its spatial band engineering is shown to be necessary and effective for the enhancement of memory window, which provides a promising scaling technology for reliable high density flash memories.