Skybridge-3D-CMOS: A Fine-Grained 3D CMOS Integrated Circuit Technology

Parallel and monolithic three-dimensional (3-D) integration directions realize 3-D integrated circuits (ICs) by utilizing layer-by-layer implementations, with each functional layer being composed in 2-D. In contrast, vertically composed 3-D CMOS has eluded us likely due to the seemingly insurmountable requirement of highly customized complex routing and regional 3-D doping to form and connect CMOS pull-up and pull-down networks in 3-D. In the current layer-by-layer directions, routing can be worse than 2D CMOS because of the limited pin access. In this paper, we propose Skybridge-3D-CMOS (S3DC), an IC fabric that shows for the first time a pathway to achieve fine-grained static CMOS circuit implementations using the vertical direction while also solving 3-D routability. It employs a new fabric assembly scheme based on predoped vertical nanowire bundles. It implements circuits in and across nanowires. It utilizes unique connectivity features to achieve CMOS connectivity in 3-D with excellent routability. As compared to the usually severely congested monolithic 3-D implementations, S3DC eliminates the routing congestions in all benchmarks studied. Further results, for the implemented benchmarks, show 56-77% reductions in power consumption, 4X-90X increases in density, and 20% loss to 9% benefit in best operating frequencies compared with the transistor-level monolithic 3-D technology.