Erasure is performed in one operation in the erase block , and a rewrite operation is performed on a bit or {TAIL ~ bits} whose threshold voltage Vt is lower than {HEAD ~ an erase operation} lower limit value  
Erasure is performed in one operation in the erase block , and a rewrite operation is performed on a bit or { TAIL ~ bits } whose threshold voltage Vt is lower than { HEAD ~ an erase operation } lower limit value
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH