In the capacitance extraction with the floating random walk (FRW) algorithm, the space management approach is required to facilitate finding the nearest conductor. The Octree and grid-based spatial structures have been used to decompose the whole domain into cells and to store information of local conductors. In this letter, the techniques with the distance limit of cell and only searching in cell's neighbor region are proposed to accelerate the construction of the spatial structures. A fast inquiry technique is proposed to fasten the nearest conductor query. We also propose a grid-Octree hybrid structure, which has advantages over existing structures. Experiments on large very large scale integration structures with up to 484 441 conductors have validated the efficiency of the proposed techniques. The improved FRW algorithm is faster than RWCap for thousands times while extracting a single net, and several to tens times while extracting 100 nets.Index Terms-Capacitance extraction, floating random walk (FRW), space management, spatial data structure, very large scale integration (VLSI) circuit.
I. IntroductionThe floating random walk (FRW) algorithm [1]-[6] is a major field-solver method for capacitance extraction. Compared with the deterministic algorithms (e.g., boundary element method [7]), the FRW algorithm has the advantages of lower memory usage, better scalability, and tunable accuracy.Today, the FRW algorithm has become the kernel of commercial capacitance solvers (such as QuickCap). With parallel computing techniques, they have been applied to the block-or chip-level extraction task in the sign-off verification of very large scale integration (VLSI) circuits. Recently, a general FRW algorithm [3] and a hierarchical FRW algorithm [4] were proposed to deal with arbitrary dielectric configuration and for a fabric-aware extraction problem, respectively. In 2013, an FRW algorithm [5] was proposed for the interconnect structure with multilayered dielectrics, where the cross-interface transition probability and weight value are precharacterized for a given process technology. The algorithm was further accelerated with a comprehensive variance reduction scheme, and has been developed to a program called RWCap [5]. Although employing an Octree-based space management approach, RWCap is not efficient for handling the large-scale structures with thousands of conductors. Another approach based on an array data structure has been used, and achieved remarkable speedup over the K-D tree based technique [6]. However, it is not well compared with other techniques, and its details are not published. In [8], several data structures were discussed to speed up the distance queries in the FRW