| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a nonvolatile semiconductor storage device which can exactly control, the threshold value and to provide the method of driving the same. <P>SOLUTION: This nonvolatile semiconductor storage device has an electrically rewritable memory cell which is composed of a laminated floating gate and control gate on the semiconductor layer, and a plurality of threshold variable pulses having a stepwise high potentials with difference of a first voltage which is required for injecting one electron into the floating gate, are respectively impressed on the control gate of the memory cell during a predetermined period. By controlling the number of electrons to be injected to the floating gate, the threshold of the memory cell can be exactly changed while suppressing the expansion of threshold distribution. By this nonvolatile semiconductor storage device, the threshold can be exactly controlled when a multi-valued bit is stored in one memory cell by the especially fine threshold control. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
