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Challenges and design choices in nanoscale CMOS

The driving force for the semiconductor industry growth has been the elegant scaling nature of CMOS technology. In this article, we will first review the history of technology scaling that follows Moore's law from the prespective of microprocessor designs. Challenges to continue the historical scaling trends will be highlighted and design choices to address two specific challenges, process variation and leakage power, will be discussed. In nanoscale CMOS technology generations, supply and threshold voltages will have to continually scale to sustain performance increase, limit energy consumption, control power dissipation, and maintain reliability. These continual scaling requirements on supply and threshold voltages pose several technology and circuit design challenges. One such challenge is the expected increase in process variation and the resulting increase in design margins. Concept of adaptive circuit schemes to deal with increasing design margins will be explained. Next, with threshold voltage scaling, subthreshold leakage power has become a significant portion of total power in nanoscale CMOS systems. Therefore, it has become imperative to accurately predict and minimize leakage power of such systems, especially with increasing within-die threshold voltage variation. A model that predicts system leakage based on first principles will be presented and circuit techniques to reduce system leakage will be discussed. It is essential to point out that this article does not cover all challenges that nanoscale CMOS systems face. Challenges that are not detailed in the main sections of the article and speculation on what future nanoscale silicon based CMOS systems might resemble are summarized.