Read only memory has two types of MOS elements - producing different information states with different threshold voltage values

摘要

Semiconductor memory region has a no. of interconnected MOS elements, each with a source and drain zone of a first conductivity type on a substrate of a second conductivity type and a gate on the subrate surface between the source and drain zones. Selected elements produce a first information state and have a zone of the second conductivity type between the source and drain zones, whilst other elements produce a second information state and have a much deeper zone of the second conductivity type between the source and drain zones. The selected elements are switched in by applying a voltage. The memory is extremely small and reliable and can be made easily, since the threshold voltage can be changed in a single stage.