Exploiting Unused Spare Columns to Improve Memory ECC

Spare columns are often included in memories for the purpose of allowing for repair in the presence of defective cells or bit lines. In many cases, the repair process will not use all spare columns. This paper proposes an extremely low cost method to exploit these unused spare columns to improve the reliability of the memory by enhancing its existing error correcting code (ECC). Memories are generally protected with single-error-correcting, double-error-detecting (SEC-DED) codes using the minimum number of check bits. In the proposed method, unused spare columns are exploited to store additional check bits which can be used to reduce the miscorrection probability for triple errors in SEC-DED codes or non-adjacent double errors in single adjacent error correcting codes (SEC-DAEC) codes.