Exhaustive and Near-Exhaustive Memory Testing Techniques and theirBIST Implementations

Abstract

In this work we investigate the problem of detection and location of single and unlinked multiple k-coupling faults in n × 1 random-access memories (RAMs). This fault model covers all crosstalks between any k cells in n × 1 RAMs. The problem of memory testing has been reduced to the problem of the generation of (n,k-1)-exhaustive backgrounds. We have obtained practical test lengths, for a memory size around 1 M, for detecting up to 6-couplings by exhaustive tests and up to 9-couplings by near-exhaustive tests. The best known test algorithms up to now provide for the detection of 5-couplings only in a 1 M memory, using exhaustive tests. Beyond these parameters, test lengths were impractical. Furthermore, our method for generation of (n,k-1)-exhaustive backgrounds yields short test lengths giving rise to considerably shorter testing times than the present most efficient tests for large n and for k greater than 3. Our test lengths are 50% shorter than other methods for the case of detecting up to 5-couplings in a 1 Mbit RAM. The systematic nature of both our tests enables us to use a built-in self-test (BIST) scheme, for RAMs, with low hardware overhead. For a 1Mbit memory, the BIST area overhead for the detection of 5-couplings is less than 1% for SRAM and 6.8% for a DRAM. For the detection of 9-couplings with 99% or higher probability, the BIST area overhead is less than 0.2% for SRAM and 1.5% for DRAM.