Increased variability in semiconductor process technology and devices requires added margins in the design to guarantee the desired yield. Variability is characterized with respect to the distribution of its components, its spatial and temporal characteristics and its impact on specific circuit topologies. Approaches to variability characterization and modeling for digital logic and SRAM are reviewed in this paper. Transistor and ring oscillator arrays are designed to isolate specific systematic and random variability components in the design. Distributions of SRAM design margins are measured by padded-out cells and minimum operating voltages for the entire array. Correlations between various components of variability are essential for adding appropriate margins to the design.
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