Delay caused by resistive opens in interconnecting lines

An accurate electrical fault characterization is required for the correct diagnosis and localization of CMOS interconnect defects. It has been traditionally accepted that a resistive open defect located at the beginning of an interconnecting line causes the maximum possible delay. The first-order approximation is sufficient to model the behaviour of high resistive opens. However, in this paper it is shown that low resistive opens do not follow this behaviour. In these cases, a second-order model is required for a more precise prediction of their defective behaviour, since the maximum delay is obtained for an intermediate location, which depends on the relationship between the open resistance, the on-resistance of the transistor network driving the defective net, the parasitic capacitances and the threshold voltage of the transistors driven by the defective net. For that purpose, an experimental circuit has been designed and fabricated where open defects have been intentionally added in a set of interconnect CMOS lines. Both simulation and experimental results on defective interconnect lines show maximum delays for opens located at intermediate positions provided that the resistance of the open is on the order of the on-resistance of the driving transistor network.