Generalized FDTD-ADI: an unconditionally stable full-wave Maxwell's equations solver for VLSI interconnect modeling

The finite-difference time-domain (FDTD) method of solving the full-wave Maxwell's equations has been recently extended to provide accurate and numerically stable operation for time steps exceeding the Courant limit. The elimination of an upper bound on the size of the time step was achieved using an alternating-implicit direction (ADI) time-stepping scheme. This greatly increases the computational efficiency of the FDTD method for classes of problems where the cell size of the three-dimensional space lattice is constrained to be much smaller than the shortest wavelength in the source spectrum. One such class of problems is the analysis of highspeed VLSI interconnects where full-wave methods are often needed for the accurate analysis of parasitic electromagnetic wave phenomena. In this paper, we present an enhanced FDTD-ADI formulation which permits the modeling of realistic lossy materials such as semiconductor substrates and metal conductors as well as artificial lossy materials needed for perfectly matched layer (PML) absorbing boundary conditions. Simulations using our generalized FDTD-ADI formulation are presented to demonstrate the accuracy and extent to which the computational burden is reduced by the ADI scheme.