| 摘要 |
<p>PROBLEM TO BE SOLVED: To virtually realize a plurality of reference cells whose threshold voltage is prescribed strictly by only one real reference cell. SOLUTION: Only one reference cell is installed inside a chip, and its threshold voltage is built precisely in a manufacturing process. Its value is set at the upper-limit value of a threshold voltage, e.g. in the erasure state of a memory cell. The gate voltage of a reference cell and the gate voltage of a memory cell are constituted so as to be capable of being set independently. The relative difference between the gate voltage of the memory cell and the gate voltage of the reference cell is changed according to a write verifying operation, an erasure verifying operation and an excess erasure verifying operation.</p> |
