Read-only/read-write memory

Abstract

An improved read-only/read-write semiconductor memory of the type that includes a semiconductor substrate with dopant atoms of a first conductivity type, a pair of spaced-apart charge storage regions at the surface of the substrate, a bit line at the surface of the substrate spaced apart from the charge storage region, respective MOSFET transistor gate regions at the surface of the substrate between the bit line and the charge storage regions, and a conductor over the storage regions; the improvement comprising dopant atoms of a second conductivity type in one of the storage regions, and dopant atoms of the first conductivity type in the other of the storage regions having a greater doping concentration than is in the body of the substrate; and circuitry for applying a read-write mode voltage to the conductor to permit charge to be stored in both of the storage regions, and for applying a read-only mode voltage to the conductor to permit charge to be stored in the one storage region and simultaneously prevent charge from being stored in the other storage region by there producing a potential barrier.