Cell Transformations and Physical Design Techniques for 3D Monolithic Integrated Circuits
3D monolithic integration (3DMI), also termed as sequential integration, is a potential technology for future gigascale circuits. In 3DMI technology the 3D contacts, connecting different active layers, are in the order of few 100 nm. Given the advantage of such small contacts, 3DMI enables fine-grain (gate-level) partitioning of circuits. In this work we present three cell transformation techniques for standard cell based ICs with 3DMI technology. As a major contribution of this work, we propose a design flow comprising of a cell transformation technique, cell-on-cell stacking, and a physical design technique (CELONCELPD) aimed at placing cells transformed with cell-on-cell stacking. We analyze and compare various cell transformation techniques for 3DMI technology without disrupting the regularity of the IC design flow. Our experiments demonstrate the effectiveness of CELONCEL design technique, yielding us an area reduction of 37.5%, 16.2% average reduction in wirelength, and 6.2% average improvement in overall delay, compared with a 2D case when benchmarked across various designs in 45nm technology node.