| 摘要 |
<p>PURPOSE:To improve the long-term reliability of a writing data by making a threshold value at a data writing time to a memory cell larger by a specified value than that at a data reading time. CONSTITUTION:A control signal 2 at a writing time is 'L', then a threshold value variation circuit F is activated and p channel transistors Q4, Q2 become parallel connection and conductance of the whole transistor becomes large and the characteristic of threshold value increases more than conventional characteristic. Namely, in a normal voltage upper limit Vmax, a threshold value at a data writing time has a margine by a specified value and a threshold value at a data writing time is made larger than that at a reading time.</p> |
