Current ratios: a self-scaling technique for production IDDQ testing

The use of a single pass/fail threshold for IDDQ testing is unworkable as chip background currents increase to the point where they exceed many defect currents. This paper describes a method of using “current signatures” which uses only simple comparisons on the tester, and which automatically scales with process variations which give a wide range of background currents. Dynamic thresholds are used, based on the ratio of maximum to minimum current. Using a single IDDQ measurement for each die, upper and lower comparator values are set, against which IDDQ for each vector in the suite is compared. Production data is presented to verify the validity of the method