Transistor-level monolithic 3D standard cell layout optimization for full-chip static power integrity

Existing transistor-level monolithic 3D (T-M3D) standard cell layouts are based on the folding scheme, in which the pull-down network is simply folded and placed on top of the pull-up network. In this paper, we propose a new layout method, the stitching scheme, targeted towards improved cell performance and power integrity. We perform extensive analysis on each layout scheme and evaluate the timing/power benefits of the stitching scheme. Since the ground and power rails overlap in the T-M3D layouts with the folding scheme, we also present a design methodology for the power delivery network of folding T-M3D ICs to evaluate the impact of the T-M3D cell layout scheme on static power integrity. Compared to 2D ICs at iso-performance, stitching T-M3D ICs show a maximum of 6% power savings, 44% area savings with only 1% more static IR-drop in the 14nm technology node while folding T-M3D ICs undergo serious degradation in static power integrity, causing a reliability issue.