A methodology for timing model characterization for statistical static timing analysis

While the increasing need for addressing process variability in sub-90 nm VLSI technologies has sparkled a large body of statistical timing and optimization research, the realization of these techniques heavily depends on the availability of timing models that feed the statistical timing analysis engine. To target at this critical but less explored territory, in this paper, we present numerical and statistical modeling techniques that are suitable for the underlying timing model characterization infrastructure of statistical timing analysis. Our techniques are centered around the understanding that, while the widening process variability calls for accurate non-first-order timing models, their deployment requires well-controlled characterization techniques to cope with the complexity and scalability. We present a methodology by which timing variabilities in interconnects and nonlinear gates are translated efficiently into quadratic timing models suitable for accurate statistical timing analysis. Specific parameter reduction techniques are developed to control the characterization cost that is a function of number of variation sources. The proposed techniques are extensively demonstrated under the context of logic stage timing characterization involving interactions between logic gates and interconnects.