Quantification of interconnect coupling mechanisms in multilayer substrates with perforated ground planes

A rigorous, full-wave electromagnetic field solver is used to investigate electromagnetic coupling mechanisms associated with the propagation of digital signals in interconnect structures with perforated reference planes. In addition to the transient modeling of crosstalk effects between lines on the same signal layer as well as lines situated on either side of a gridded plane, higher-order electromagnetic effects, caused by the periodic nature of the ground plane perforations, and responsible for potential electromagnetic interactions between distant interconnect lines, are identified. In particular, it is shown that surface waves, with zero cut-off frequency, can be supported by the gridded planes. Such waves are excited at places where the interconnects exhibit discontinuities (e.g. a via through the perforated plane) and, since they have zero cut-off frequency, they give rise to noise pulses propagating throughout the substrate and leading to undesirable interference effects. Numerical experiments are presented to illustrate these surface waves and examine their dependence on the size of the perforations in the ground plane.