A High Density EPROM Cell, and Array

Replacing all existing mask programmable ROMs with EPROMs is especially attractive in a VLSI wafer fabrication environment. Elimination of the custom masks would make it easier to automate the wafer processing, would reduce inventory, and would permit redundant designs. However the increased processing complexity and larger cell area of existing EPROM memory cells have so far kept the cost/bit of EPROMs higher than mask programmable ROMs. This paper describes a new EPROM cell which is not only smaller than existing EPROM cells but is even smaller than most existing mask programmable ROM cellTs.his new cell and array require a minimum number of masking steps and therefore could permit fabrication of VLSI EPROM's with a lower cost/bit than mask programmable ROMs.