A new combination-erase technique for erasing nitride based (SONOS) nonvolatile memories

A new technique of erasing nonvolatile memory (NVM) devices based on nitride storage (SONOS) with bottom oxide thickness in the range of 30 A has been developed. Oxide thickness in this range is necessary to minimize the undesirable effects of gate disturb while still enabling a low-voltage operation to maximize the cost benefit of SONOS memories. To erase such bitcells, FowlerNordheim tunneling (FNT) is preferred over hot-hole injection (HHI) due to the less damaging nature of FNT. However, FNT alone cannot be used to erase the device completely due to erase saturation limitations. Hence, the new "combination-erase" technique combines both FNT and HHI erase to achieve a fast and controlled erase. Furthermore, by using FNT erase at higher field conditions, and HHI erase at lower field conditions, the reliability of the bitcell is also improved.