METHOD FOR DISCRIMINATING NON-VOLATILE MEMORY ELEMENT BY INADEQUATE SUBTHRESHOLD VALUE GRADIENT OR WEAK TRANSCONDUCTANCE

摘要

PROBLEM TO BE SOLVED: To provide a method for discriminating cells which have inadequate subthreshold values and weak transconductances.

SOLUTION: A first group technique focuses the lens on inadequate subthreshold value behaviors of deteriorated memory elements by carrying out cycle operation of the cells, then programming them to a potential higher than earth potential, and then reading the cells with a control gate voltage lower than a threshold voltage for the potential in order to see whether the cells are conducted. A second group practice form focuses the lens on weak transconductance behaviors by reading the programmed cells with a control gate voltage higher enough than the threshold voltage. In a third group practice form, voltage level in source-drain regions of the memory elements is varied. While current vs. voltage curves of good memory elements are rather stable under such a shift in bias condition, current vs. voltage curves of the deteriorated memory elements show bigger shifts. Thereby the discrimination between the good memory element group and the failure memory element group becomes possible.

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