SEMICONDUCTOR MEMORY DEVICE

摘要

PROBLEM TO BE SOLVED: To prevent the destruction of data and to prevent the destruction of a memory device itself, by sensing the time point when the temperature of a using environment has reached a specified value or when the value of the function guided from the temperature of the using environment and the time has reached a specified value. SOLUTION: A first sensing circuit 10 measures environment temperatureand and is set so that the output voltage of the circuit 10 reaches a first specified value when the temperature becomes To. Then, a second judging circuit 12 judges whether the data of each bit of a memory matrix 14 are in the writing state or the erasing state through a decoder 15. For the bit, which is judged by the circuit 12 so that the bit is in the writing state, rewriting is performed. Even if threshold voltage of the bit, wherein the data are written in a high temperature environment, is decreased, the threshold voltage rises up by the rewriting. Furthermore, the circuit 13 prevents the excessive writing so that the threshold voltage does not exceed the normal value when the rewriting is performed. In this way, the environment temperature is sensed, the memory data are rewritten and the destruction of the memory data is prevented.