Improving Detailed Routability and Pin Access with 3D Monolithic Standard Cells

We study the impact of using 3D monolithic (3DM) standard cells on improving detailed routability and pin access. We propose a design flow which transforms standard rows of single-tier "2D" cells into rows of standard 3DM cells folded into two tiers. The transformation preserves layout characteristics such as overall area and number of metal layers for signal routing (i.e., M2 and above). It also creates redundant pins and free routing tracks in the two tiers used by the 3DM cells. We then propose an Integer Linear Program which routes as many nets as possible on the free 3DM routing tracks, leaving the rest of the nets to be routed via a standard global and detailed router on the metal layers dedicated for signal routing. Our experiments show significant improvement in detailed routability metrics using 3DM cells compared to using 2D standard cells.