A novel operation method to avoid over-erasure in a scaled trapping-nitride localized charge storage flash memory cell and its application for multilevel programming

By using the charge pumping technique, it was found that the injected-hole occupied percentage increases with respect to the whole channel, and overerasure thus happens in a scaled trapping-nitride storage Flash memory cell. Such overerasure can be avoided or can be recovered if the cell is suitably biased during the erase operation. Moreover, the erase threshold voltage can be well controlled by the applied erase gate voltage. The reason is that both the channel-hot electrons and the band-to-band tunneling-induced hot holes would inject at the same time and are in balance as a specific surface potential is achieved. Based on this study, a self-limited soft program, as well as a self-saturated erase scheme, is proposed. Applications of this concept to multilevel programming are also demonstrated.