NONVOLATILE SEMICONDUCTOR MEMORY AND METHOD FOR OPERATING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a nonvolatile memory device having the optimum 2-bit cell structure.

SOLUTION: The method for programming a memory cell comprises a step for setting the memory cell to an initial state of a first gate threshold voltage and a step for executing processing sequence, in which the processing sequence includes a step for applying a voltage bias between a gate and a first junction area so that an electron hole migrates toward a trapping layer and is retained in the trapping layer and a step for evaluating a readout current generated in response to the voltage bias to determine whether a second gate threshold voltage is reached or not. The second gate threshold voltage is lower than the first gate threshold voltage. The processing sequence is repeated plural times, by varying the voltage bias between the gate and the first junction area once or more, until a second voltage bias is reached and the memory cell is in a program state.

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