| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve the reliability of storage of multibit data by programming one data state so as to have a threshold voltage distribution and making differences among adjacent distributions corresponding to respective data states uneven. SOLUTION: States in which two-bit data are enabled are distributed in a voltage equal to or lower than a critical threshold voltage Vmax. Threshold voltage distributions corresponding to respective states are 0.4 V. The difference between a lower threshold voltage distribution (a) and a higher threshold voltage distribution (b) and the difference between b' and b" are not equal on the basis of respective selection voltages Vg1, Vg2 and Vg3. Moreover, the higher the threshold voltage is, the larger the difference between b and b', the difference between b' and b" become. Consequently, a bit failure phenomenon in which electric charge stored on a floating gate is induced by an inverse F-N tunnelling current and various leakage sources can be prevented.</p> |
