Impact of systematic spatial intra-chip gate length variability on performance of high-speed digital circuits

  • Authors:
  • Michael Orshansky;Linda Milor;Pinhong Chen;Kurt Keutzer;Chenming Hu

  • Affiliations:
  • University of California, Berkeley, CA;eSilicon Corporation, Berkeley, CA;University of California, Berkeley, CA;University of California, Berkeley, CA;University of California, Berkeley, CA

  • Venue:
  • Proceedings of the 2000 IEEE/ACM international conference on Computer-aided design
  • Year:
  • 2000

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Abstract

Using data collected from an actual state-of-the-art fabrication facility, we conducted a comprehensive characterization of an advanced 0.18μm CMOS process. The measured data revealed significant systematic, rather than random, spatial intra-chip variability of MOS gate length, leading to large circuit path delay variation. The critical path value of a combinational logic block varies by as much as 17%, and the global skew is increased by 8%. Thus, a significant timing error (∼25%) and performance loss takes place if variability is not properly addressed. We derive a model, which allows estimating performance degradation for the given circuit and process parameters. Analysis shows that the spatial, rather than proximity-dependent, systematic Lgate variability is the main cause of large circuit speed degradation. The degradation is worse for the circuits with a larger number of critical paths and shorter average logic depth. We propose a location-dependent timing analysis methodology that allows to mitigate the detrimental effects of Lgate variability, and developed a tool linking the layout-dependent spatial information to circuit analysis. We discuss the details of the practical implementation of the methodology, and provide the guidelines for managing the design complexity.