Observation of fast erase due to enhanced generation of holes caused by electron impact ionization

This letter describes an enhanced erase mechanism in flash memory cells due to impact ionization induced generation of holes. The increased population of holes is initiated by the impact ionization of electrons in the collector-base region of a parasitic bipolar transistor. Electrons injected from the emitter (drain) of a parasitic n-p-n bipolar transistor into the base (substrate) can drift to the collector (source) where the high electrical field in the collector-base space charge region causes impact ionization and carrier multiplication. The impact ionization generated holes that gain enough energy to overcome the oxide barrier can be injected into the floating gate, resulting a very fast erase.