Characterization and modeling of multilayer interconnections for high-speed digital systems

Abstract

The frequency-dependent characteristics of lossy interconnections such as on-chip metallization and wiring in multichip modules are characterized rigorously by 2D full-wave analyses using dyadic Green's functions. The frequency-dependent complex propagation constants and complex characteristic impedances for both single and coupled lossy transmission lines are obtained. Such transmission line parameters can be used in specialized circuit simulators to accurately characterize the lossy metal interconnections used in high speed and high frequency circuits. Effects of the frequency-dependent metal loss on signal propagation and coupling are then studied by circuit level simulations. The effects of common 3D structures in multilayer interconnections, such as vias and ground gaps, are studied by a 3D electromagnetic field solver using the transmission line matrix method and by experiments of large scale models. It is observed that electromagnetic waves that propagate in multilayer interconnections can excite other electromagnetic modes when they encounter discontinuities. This phenomenon, the excitation of different electromagnetic modes at discontinuities, is called mode conversion. Accurate and efficient equivalent circuit models of vias and ground gaps are developed and validated by experimental data. The mode conversion effects of multiple 3D discontinuities are investigated in detail. It is found that under certain conditions, the cumulative effects of unwanted mode conversion can be significant or catastrophic. Hence, layout of such interconnection structures must be carefully planned and accurately modeled during early design stages. With the aid of the developed models, design methodologies are investigated, such as the suppression of the unwanted mode conversion effects.