| 摘要 |
<p>PROBLEM TO BE SOLVED: To prolong the service lifetime of a nonvolatile semiconductor storage device by extending restrictions on write and erasure cycles. SOLUTION: In a nonvolatile semiconductor storage device, which is provided with a floating gate 3 and a control gate 8 when erasing information written in the floating gate 3 by discharging charges (electrons) to the control gate 8 from the floating gate 3 through the use of tunnel effect, an erasure gate 17 used exclusively for erasure is provided in addition to the control gate 8, so that the gate being used for erasure is switched to the erasure gate 17 from the control gate 8 by discriminating the limit of writing and erasure cycles, based on the value of the current of a memory cell A is an erased state at operating for read-out, are performed on the memory cell A.</p> |
