A study on the radiation hardness of flash cell with horn-shaped floating-gate

Abstract

The effects of radiation on the characteristics of split-gate electrical erasable programmable read only memory (EEPROM)/flash cells with recently-proposed horn-shaped floating gates are studied in terms of cell read current; data retention, cycling endurance, program/erase efficiency, threshold voltage and junction leakage. Our results show that the cells appear to survive after 1 Mrad (Si) Co-60 irradiation. Moreover, the after-irradiation cell read current actually increases in the ''erase'' (i.e., low-threshold voltage, high-conducting) state (i.e., improves), albeit the cell read current also increases in the ''program'' (i.e., high-threshold voltage, low-conducting) state (i.e., a degradation). Our results also show that, despite an improvement in the initial read current in the ''erase'' state immediately after radiation, the write/erase cycling endurance of the flash cells is significantly impeded after irradiation, due to a much faster ''window closure'' rate in the ''erase'' state, although the cell read current is found to remain relatively stable in the ''program'' state after cycling.