Nonvolatile semiconductor memory

Claim 1

A metal-nitride-oxide semiconductor memory device comprising: a semiconductor n-type substrate; an elongated p-type source region in the surface of said substrate; an elongated p-type drain region in the surface of said substrate running parallel to said elongated source region; a first gate insulation film consisting of a very thin oxide film formed on a substrate surface region between said elongated source and drain regions; a silicon-nitride film formed on said first gate insulation film; first and second metal-oxide-semiconductor field-effect transistors, the source and drain of each of said transistors being said elongated source and drain regions, said transistors being positioned respectively on either side of said first gate insulation film and having respectively second and third gate insulation films between said elongated source and drain regions; source, drain, and first, second and third gate electrodes respectively formed on said elongated source and drain regions, and said first, second and third gate insulation films, said second and third gate electrodes being separated from said first gate electrode; means for effecting writing-in of information by ejecting carriers from said substrate surface region between said source and drain regions into electron traps in said silicon-nitride film; means for impressing ground potential to said substrate and to said first gate electrode and a predetermined negative potential to said source, drain and second and third gate electrodes so as to form a depletion layer which surrounds completely the substrate surface region under said first gate insulation film at the time of effecting writing-in of information; and means for allowing the potential of said substrate surface regions completely enclosed by said depletion layer to approach that of said source and drain regions by injecting carriers into said surface region.