Within-die delay variability in 90nm FPGAs and beyond

Semiconductor scaling causes increasing and unavoidable within-die parametric variability. This paper describes accurate measurement techniques for characterising both systematic and stochastic delay variability in FPGAs. Results and analysis are presented from measurements made on a sample of 90nm devices, showing that delay per logic element varies stochastically by +/- 3.54% on average over the set. The delay also varies by up to 3.66% across a single die from correlated sources of variability. The results are extrapolated to determine the impact at future technology nodes. The predicted significant performance degradation that variability will cause demonstrates the importance of new circuit or system design techniques to cope with variations in future FPGAs.