Importance

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Abstract

A nonvolatile semiconductor device is provided, which does not need excessive writing or verification operations, except for the originally required writing and verification operations. The data is arranged in the order from the lowest '11', '10', '01', to the highest '01'. Four valued writing data are set in the latches 1 and 2 by data signals DL1 and DL2, and the latch 3 is initialized to '0'. Writing is executed by three stages, and before writing at each stage, if the latch 3 is '0', the data is transferred to the latch 2. Writing is only executed when any one latch is '0', and the latch is changed to '1' after the verification is completed. First, writing is executed up to the threshold value of the data '01', except the data '11' where the latch 2 is '0'. Next, writing is executed for the data '00' and '01' up to the threshold value of the data '00', where the latch 1 is '0'. Finally, the data '01' where the latch 2 is '0' is written up to the threshold value of '01'.

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First Claim