METHOD AND APPARATUS FOR SUPPRESSING OVERERASURE OF NONVOLATILE SEMICONDUCTOR DEVICE

摘要

PROBLEM TO BE SOLVED: To suppress overerasure surely by injecting electrons in the way of erasure operation where electrons are emitted from a floating gate. SOLUTION: When an erasure pulse is applied, a voltage of about 12V is applied to the source 18 and the control gate(CG) 17 is grounded. When the drain 19 is brought into OPEN state, electrons in a floating gate 16 are attracted to the source 18 through FN tunneling. When a gate high pulse is applied, the source 18 is grounded and a voltage of about 12V is applied to the CG and then the drain 19 is brought into OPEN state thus injecting electrons into the FG 16 from a substrate 15. Consequently, fluctuation is suppressed in the distribution of threshold voltage by applying a gate high pulse after applying an erasure pulse. Overerasure is suppressed by continuing the erasing operation.