In multi-layered power/ground (P/G) networks, to connect the whole network together, vertical vias are usually placed at intersections between metal wires of adjoining layers. In this paper, a deep study about the design of vertical vias is presented. First we present an efficient heuristic algorithm based on sensitivity analysis to optimize via allocation in early design stage. Compared with even allocation, averagely our algorithm is capable of reducing worst voltage drop by 8.43% while using the same or even less number of vias. Also, adjoint network method is utilized and significantly improves the efficiency of our algorithm. Next, we demonstrate that by linking metal wires of nonadjacent layers, cross-layer vias are powerful in eliminating "hot" areas which suffer from large voltage drop on bottom layer. A similar heuristic algorithm is also developed for the addition of cross-layer vias.
['Shuai Li', 'Jin Shi', 'Yici Cai', 'Xianlong Hong']
Vertical via design techniques for multi-layered P/G networks