Accurate electromagnetic full-wave modeling for interconnects in semiconductor integrated circuits
Zhang, Lu (2007) Accurate electromagnetic full-wave modeling for interconnects in semiconductor integrated circuits. PhD thesis, Iowa State University.
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Semiconductor-based integrated circuits have become the mainstream for very-large-scale integration systems such as high-speed digital circuits, radio-frequency integrated circuits, and even monolithic microwave integrated circuits. The shrinking feature size and increasing frequency promote high integration density and interconnection complexity that demand high-accuracy modeling techniques. The current design paradigm has shifted from the transistor-driven design to the interconnect-driven design. Thus the accurate electromagnetic full-wave modeling of on-chip interconnect becomes critical for the computer-aided design tools to analyze the overall system performance. In this research, the full-wave spectral domain approach is implemented to investigate the electromagnetic properties of multilayered transmission lines with semiconductor substrates. In particular, finite thin metallization components, such as the thin metal ground layer and signal strips, are focused on. The thin metal ground layer is generally designed as a shield or a ground plane to depress the coupling and noise from neighboring components. But its fabricated thickness is often a small fraction of one micron, which may allow electromagnetic fields to penetrate through at some low frequencies. Such electromagnetic leakage phenomena play a significant role in the overall dispersive performance of transmission lines, and their consideration is inevitable. For the spectral domain approach, the metallization layer can be rigorously modeled as a dielectric with a complex permittivity. However, due to the large conductivity of metal, the conventional transfer matrix method has potential overflow problems in obtaining the multilayered Green's function. In our research, a new formulation of the cascaded matrix is developed to overcome such numerical difficulties. Based on this formulation, the complete characteristics of multilayered transmission lines with thin metallization components are studied by parameters like the propagation constant, attenuation per unit length, field distribution, characteristic impedance, transient response, and extracted resistance, inductance, capacitance, and conductance of equivalent circuits. The parallel-plate waveguide model is applied to study a metal-insulator-metal-semiconductor structure. The first- and second-order low-frequency approximations for the fundamental propagation mode are derived with corresponding equivalent circuit models. In addition, other approximate models for the thin metal ground are compared numerically to assess their validity. Two transmission lines with the metal-insulator-metal-semiconductor and the metal-insulator-metal-insulator structures are analyzed. Numerical results indicate that the thin metallization components have significant impacts on the propagation characteristics. The thin metal layer can enhance or even excite the slow-wave mode. Thus, it is necessary to take these effects into account to achieve accurate and reliable analysis of integrated circuit interconnects from dc to millimeter-wave frequencies.
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