Performance improvement of flash memories with Hf O x N y ∕ Si O 2 stack tunnel dielectrics

The operating characteristics of flash memory devices with tunnel dielectrics comprising a hafnium oxynitride ( Hf O x N y ) layer or a hafnium oxynitride/silicon dioxide ( Hf O x N y ∕ Si O 2 ) stack, annealed at various temperatures, were studied. The present work indicates that flash memory devices with a Hf O x N y ∕ Si O 2 stack tunnel dielectric have a higher program/erase speed and better reliability than those with a single Hf O x N y layer. The stack tunnel dielectric composed of a thick Hf O x N y layer and a thin Si O 2 layer exhibits an even better performance in the flash memory operation. In addition, devices with Hf O x N y ∕ Si O 2 stack tunnel dielectrics annealed at 850 ° C show the best performance in terms of the program/erase speed, charge retention, and read disturbance.