Block redundancy for memory array

Abstract

Block redundancy is utilized to improve yield and lower die cost for an electrically programmable read only memory (EPROM). The EPROM is organized 8Kx8 with four primary memory blocks on each side of a central row decoder. Each block includes an array of memory cells, column select, column decode, sense amp, data buffer and other overhead circuitry. One block of redundant circuitry is also provided for each set of four blocks and includes a redundant memory matrix, a redundant column decoder, a redundant column select, a redundant sense amp and a redundant data buffer. Incorporated within each primary memory block is a multiplex logic circuit which is independently programmable to selectively disconnect the associated primary memory block and substitute the redundant memory block, including the redundant column decoder, column select, sense amp and data buffer. Each multiplex logic circuit includes a polysilicon fuse which is permanently programmable from a closed to an open circuit condition by applying a high voltage to the external data bit terminal which corresponds with the defective memory block cells. According to this arrangement, for each group of blocks, one out of four primary memory arrays including the associated column select, column decoder, sense amp and data buffer, may be replaced during wafer testing and after encapsulation.