Near-optimal March Tests for Three-Cell and Four-Cell Coupling Fault Models in Random-Access Memories

This research work addresses the problem of testing n×1 RAMs in which complex models of unlinked static three or four-cell coupling faults are considered. As in other works, it is assumed that only physically neighboring memory cells could be involved in a three or four-cell coupling fault. For this reason, these fault models can also be considered to be of the neighborhood pattern sensitive type. As extensions of the well-known model of all unlinked static two-cell coupling faults, the fault models we address are complex including faults sensitized by a transition write operation as well as faults sensitized by a non-transition write or a read operation. For these complex models, near-optimal multirun march tests are proposed. This optimality assessment is based on the fact that, for any group of cells corresponding to the considered fault model, the state graph is completely covered, and each arc is traversed only once, which means that the graph is of the Eulerian type. Additional write operations are only required for data background changes.