Representing topological structures for 3-D floorplanning

3-D VLSI circuit is becoming a hot topic because of its potential of enhancing performance, while it is also facing challenges such as the increased complexity on floorplanning and placement. Efficient 3-D floorplan representations are needed to handle the placement optimization in new circuit designs. We review and categorize some state-of-the-art 3-D representations, and propose a twin quaternary tree (TQT) model for 3-D mosaic floorplans, extending the twin binary tree. Differences between 2-D and 3-D mosaic floorplans are discussed and some 3-D properties not existing in 2-D are revealed. Though the efficiency of the twin tree for optimization heuristics is still an open question, insights from the discussions and conclusions can be helpful for 3-D physical design.