On macro-fault: a new fault model, its implications on fault tolerance and manufacturing yield

A macro-fault is defined as a group of signal faults such that the errors induced cannot be observed unless two or more faults (either permanent or temporary) in the group happen simultaneously. Since adding a redundant (alternative) wire for an existing (target) wire can mask some certain faults of these two wires mutually, a macro-fault can be formed by redundant wire addition. The faults that are dominated by or equivalent to the masked faults are also included in the macro-fault. As the feature size of integrated circuit technologies continue to scale down, manufacturing fault-free chips is getting more difficult and fault tolerance techniques will become more critical. In the past, redundancy has been adopted for memory for improving fault tolerance. For critical circuit components, even the costly triple modular redundancy techniques have to be applied. In this work, we study the implications of our new fault model, macro-fault, on the potential impact on fault tolerance and manufacturing yield. Based on the findings, a heuristic approach based on redundant wire addition is designed for improving fault tolerance. The approach can be incorporated with other fault tolerance techniques to form a hierarchical cross-layer fault tolerance scheme.