Method and apparatus for protecting content of semiconductor non-volatile memory and memory itself

摘要

Described are method and apparatus for protecting content of a semiconductor non-volatile memory and a semiconductor non-volatile memory itself, the semiconductor non-volatile memory being constituted by, for example, a flash memory, so that a reduction in a life time of the non-volatile memory due to an excess number of times a refresh (rewrite) operation can be prevented. For example, a first data deterioration determining voltage V1 is applied via a row decoder to one of word lines to which a selected bit is connected to determine whether the selected bit is turned on and a second data deterioration determining voltage V2 is applied to the same word line to determine whether the selected bit is turned off. The results of the determinations are stored in a second memory unit. If the selected bit is turned on in the former result and is turned off in the latter result, a control circuit determines that the data in the selected bit is deteriorated and carries out the refresh operation for the selected bit. The value of V1 is set which falls in a voltage range from a relatively high threshold voltage to a rated power supply voltage (VCC) and the value of V2 is set which falls in a voltage range from the power supply voltage (VCC) to a relatively low threshold voltage.