Analysis of Layout Density in FinFET Standard Cells and Impact of Fin Technology

In this paper, the layout density of three-terminal FinFET logic circuits is extensively analyzed. As opposite to previous works, which are focused either on single devices or simplistic circuits, this analysis explicitly includes the geometric constraints that are imposed by the standard cell approach. The impact of the fin technology is analyzed by comparing the lithography- and spacer-defined approaches, as well as evaluating the dependence of layout density on the fin height. Results show that FinFET standard cells have a layout density that is better than bulk cells even for moderately tall fins. The fin height is also shown to be a powerful knob to improve the layout density in FinFET cells. Analysis also shows that the usually claimed 2X density improvement of the spacer-defined technology compared to the lithography-defined is dramatically reduced in real standard cells, and can be negligible for tall fins. All results are justified through considerations at the physical level of abstraction. Various versions of a 32-nm 44-gate library are laid out to carry out the analysis.