Programmable and erasable MOS memory device

Claim 1

An electrically programmable and electrically erasable MOS memory device comprising, a semiconductor substrate of a first conductivity type with at least one active memory area defined therein, a field isolation oxide layer disposed on the substrate in all nonactive areas, a plurality of implants of a second conductivity type extending to a first depth, having a first doping concentration and having edges spaced lengthwise apart in said active memory area, said implants defining first and second channels therebetween, a program-and-erase implant of said second conductivity type extending to a second depth, greater than the first depth, and located in said active memory area, said program-and-erase implant overlapping one of said plurality of spaced apart implants in said active memory area and extending into said second channel, a relatively thin oxide tunnel layer disposed over the entire second channel including over that portion of said program-and-erase implant which extends into said second channel, a relatively thick oxide layer disposed over the entire first channel, a polysilicon floating gate disposed over said thin oxide tunnel portion above said second channel, said floating gate having opposed edges, one of the edges aligned with one edge of two of said plurality of implants of the second conductivity type, said floating gate also covering said portion of said program-and-erase implant which extends into said second channel with said thin oxide tunnel portion therebetween, said thin oxide tunnel portion underlying the entire length of said floating gate, a polysilicon select gate disposed over said relatively thick oxide layer above said first channel, thereby forming a select transistor, a interpoly insulation layer of substantially uniform thickness disposed over said floating gate, and a control gate disposed over said interpoly insulative layer and capacitively coupling to said floating gate for enabling tunneling of charge carriers between said program-and-erase implant and said floating gate through said thin oxide tunnel portion.