Investigation of the soft-write mechanism in source-side injection flash EEPROM devices

The soft-write effect which occurs when reading the content of a source-side injection (SSI) flash EEPROM cell has been identified and thoroughly investigated. This effect is caused by an electron injection mechanism which has the same physical origin as the enhanced (or source-side) hot-electron injection that is used for fast flash EEPROM programming. A procedure for the prediction of the associated soft-write lifetime is proposed, subsequently applied to a state-of-the-art split-gate SSI cell, and found to be noncritical for a reliable device operation. Therefore, source and drain do not have to be interchanged during the read-out operation with respect to the programming operation, and the traditional forward read-out scheme can be maintained for SSI flash memories.<>