Investigation and impact of LDD variations on the drain disturb in normally-on SONOS NOR flash device

In this paper, we elaborated non-localized drain disturb (DD) in the normally-on silicon-oxide-nitride-oxide‑silicon (SONOS) flash device by experiments and simulations. It was found that a peak value of vertical tunneling oxide (TO) E-Field at channel center occurs along with DD stress time. This indication was ascribed to different charge de-trapping rate at channel-inside and drain-side region. Additionally, the impact of lightly doped drain (LDD) on the DD immunity was fully investigated. It indicated that large dose and high energy of LDD would degrade DD immunity and that LDD optimization achieves better tradeoff between on-current and DD immunity. Finally, this paper confirmed that LDD with larger dose and lower energy is preferable for better tradeoff between on-current and DD immunity. It also reveals that the tradeoff is still inevitable to achieve ultrahigh DD immunity.