Degradation mechanism of flash EEPROM programming after program/erase cycles

The mechanism of degradation of flash EEPROM cell characteristics caused by program operation with the channel hot electron injection after program/erase (P/E) cycles are investigated. To clarify the relation between the degradation and oxide damage such as interface-states and oxide charges, the charge-pumping (CP) technique, transconductance (G/sub m/) measurements and cell endurance measurements are performed. In the degradation, a reduction of electron injection into the floating gate and a reduction of the G/sub m/ should be considered separately. The reduction of electron injection into the floating gate is found to be caused mainly by the interface-states located in the drain overlap region, not by charges trapped in the oxide. These interface-states are created during the initial step of program operation. On the contrary, a reduction of G/sub m/ is caused mainly by interface-states located around the drain edge. These are created during the final step of program operation.<
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