Rram Spare Allocation

RRAM (Redundant Random Access Memory) is a RAM with redundant spares included in the chip. Because of the row/column organization of memory cells in RAMs, these spares are organized as rows and columns. Memory cells which are faulty can be repaired by the spare rows, spare columns and their combinations. Because additional cost of incorporating spares and repairing, it is usually advantageous to have as less number of spare rows and columns as possible in the chip. Having too less number of spare rows and columns, on the other hand, make a larger proportion of chips unusable and thus the yield is aaected. What the semiconductor industry is looking for are good repair schemes which emphasize on complete coverage of faults using minimum number of spares and the overlapping of testing and repair analysis. The latter provides many advantages. Any unrepairable chip is possibly scanned out before the whole analysis nishes. Also, the time to repair chips can be lowered as part of the a analysis is completed in the stage of testing. The combined eeect is increased usable yield in a shorter production time and thus a higher throughput. In this paper, an on-line testing scheme for row/column weight sensitive faults is presented. Such a fault coverage scheme is expected to cover most of the possible faults and to report unrepairability as early as possible.