Partial breakdown of the tunnel oxide in floating gate devices

The reliability of thin oxide used for charge tunneling in the erase/program operation of floating gate devices, e.g. EEPROM, is examined. It is frequently observed in the simulated Erase operation that the oxide can break down partially, which implies localized physical damage and oxide thinning at and/or near the anode, i.e. the Si/SiO2 interface, before a complete breakdown occurs. After the partial breakdown, the negative-gate-biased Fowler-Nordheim tunneling current essentially arises at a lower gate bias, with the shifted amount depending on the degree of oxide thinning. In contrast, the positive-gate-biased characteristic exhibits a more drastic change, usually similar to an electric short, obviously due to the combining effect of field enhancement, lower barrier and high density of charge traps near the damaged site. (C) 1997 Elsevier Science Ltd.