PROM Cell made with an EPROM process

A floating-gate PROM cell has been developed which is electrically the same as an EPROM cell but which is not erasable with UV radiation. A metal shield is fabricated so that it surrounds the transistor and increases the time for erasure consistently beyond the 168 hour goal. A practical result of this work is that the shielded PROM cell is used on a 128K EPROM to provide redundancy circuits with information defining which rows in the array are to be replaced by redundant rows.