An efficient four layer over-the-cell router

Several Over-the-Cell (OTC) routing algorithms have been proposed for two and three layer processes. All the existing OTC routers assume that the terminals are laid out in a specific predetermined fashion. These restrictions on the terminals complicate the task of cell design and increase the width of the cells. In this paper, we develop a four layer OTC router which allows arbitrary terminal locations. Freed from fixed terminal placement restrictions, cell designers can aim to design with minimum width. Our router has been implemented and tested on several circuits. For most of the circuits, it obtained channel-less layouts