Retention characteristics of hole-injection-type EEPROM

The retention characteristics of FAMOS-type EEPROM using avalanche injection of holes for ERASE operation were analyzed. The avalanche-injected holes into the SiO2gate oxide are likely to be trapped at the defects in the gate oxide before arriving at the floating gate. Some samples show that the threshold-voltage shift due to trapped holes versus the threshold voltage shift due to the total holes injected into the oxide comes up to 80 percent. The retention characteristics of trapped holes are poor. By detrapping these holes, the drain voltage of a FAMOS-type device is increased. The resultant acceleration of the unintentional writing due to the channel current-induced hot electrons may be a dominant factor in the retention characteristics.