NON-VOLATILE SEMICONDUCTOR MEMORY AND SCREENING METHOD FOR ITS MEMORY CELL

摘要

PROBLEM TO BE SOLVED: To prevent that a normal memory cell is screened by detecting such an abnormal cell that a normal memory cell is guided to an over-erasion state. SOLUTION: External power source voltage Vpp is supplied to a control gate of a memory cell 32 after memory cells 32 are erased en bloc or erased in block, while internal power source voltage Vcc is supplied to a control gate of a reference value cell 33 of a constant threshold value, magnitude of a drain current Id(ARR) flowing in the memory cell 32 and a drain current Id(SRC) flowing in the reference value cell 33 are compared by a sense amplifier 31 and an abnormal cell is detected. After detecting an abnormal cell, it is detected whether a memory cell considered as normal is over-erased or not.