AN ALGORITHM TO TEST RAMS FOR PHYSICAL NEIGHBORHOOD PATTERN SENSITIVE FAULTS

Abstract

State-of-the-art memory chips are designed with spare rows and columns for reconfiguration purposes. After a memory chip is reconfigured, physically adjacent cells may no longer have consecutive logical addresses. Test algorithms used at later stages for the detection of physical neighborhood pattern sensitive faults have to consider the fact that the address mapping of the memory chip is no longer available. Furthermore, RAM decoders are designed with a view to minimize the overall silicon area and critical path lengths. This can also result in designs in which physically adjacent rows (and columns) are not logically adjacent. In this paper, we present new test algorithms to detect 5-cell and 9-cell physical neighborhood pattern sensitive faults in dynamic RAMs, even if the logical and physical addresses are different and the physical-to-logical address mapping is not available. These algorithms have test lengths of O(Nr10g3M4) for N-bit RAMs, and also detect other faults such as stuck-at and coupling faults. The algorithms depend on the development of an efficient 3-coloring algorithm that michromatically colors all the triplets among a group off n objects in at most r1og34 coloring steps.