NONVOLATILE SEMICONDUCTOR MEMORY

摘要

PROBLEM TO BE SOLVED: To reduce the electric field applied to a tunnel film by changing the load characteristic in accordance with a threshold value of a memory cell when electrons are emitted from a floating gate of the memory cell. SOLUTION: A comparator 7 compares a cell read data SD from a sense circuit 5 and an expected value data ED after a first stage electron emission, and sends a comparison result COMP to an electron emission operation control circuit 6. When the circuit 6 detects that all memory cells pass to emit electrons at the first stage, the circuit 6 outputs a second electron emission signal EES2 to a source voltage control circuit 10 and a verification voltage generation circuit 9. The circuit 9 outputs an electron verification voltage Vver to a row decoder 2 so as to judge by a threshold value of a memory cell whether or not electrons of a predetermined count are emitted. The circuit 10 supplies in compliance with the signal EES2 a source voltage Vsc lower than at the first stage to a source of a memory cell array 1 to perform second stage electron emission.