Improvement of Mixed Track - Height Standard-Cell Placement

In sub-Snm nodes, track-height of standard cells must be aggressively scaled down while preserving design PPA. This requirement brings the challenge of placing a set of cells that have mixed track-heights, subject to the constraint that cells with the same height must be placed together in an “island” of cell rows. We apply integer linear programming (ILP) to solve the row assignment problem and improve the runtime of ILP with clustering, using a cost function that combines half-perimeter wirelength and displacement from a starting unconstrained placement. Considering the row assignment solution, we define fence-regions, which enable an existing place-and-route (P&R) tool to place the cells while considering the row-island constraints. Experimental results show that our proposed method can on average reduce final-routed wirelength by 8.5% and total power by 3.3 %, with worst negative slack and total negative slack reductions of 24.0% and 13.0%, compared with the previous state-of-the-art method [10].