Abstract:
With increasing operating frequencies in CMOS RF/microwave integrated circuits,
the performance of on-chip interconnects is becoming significantly affected by the lossy
substrate. It is the purpose of the first part of this thesis to develop a rigorous field
theoretic analysis approach for efficient characterization of single and multiple coupled
interconnects on silicon substrate, which is applicable over a wide range of substrate
resistivities. The frequency-dependent transmission line parameters of a microstrip on
silicon are determined by a new formulation based on a quasi-electrostatic and quasi-magnetostatic
spectral domain approach. It is demonstrated that this new quasi-static
formulation provides the complete frequency-dependent interconnect characteristics for
all three major transmission line modes of operation. In particular, it is shown that in the
case of heavily doped CMOS substrates, the distributed series inductance and series
resistance parameters are significantly affected by the presence of longitudinal substrate
currents giving rise to the substrate skin-effect. The method is further extended to
multiple coupled single and multi-level interconnect structures with ground plane and
multiple coupled co-planar stripline structures without ground plane. The finite conductor
thickness is taken into account in terms of a stacked conductor model. The new quasi-static
approach is validated by comparison with results obtained with a full-wave spectral
domain method and the commercial planar full-wave electromagnetic field solver
HP/Momentum®, as well as published simulation and measurement data.
In the second part of this thesis, coupled planar optical interconnect structures are
investigated based on a rigorous field theoretic analysis combined with an application of
the normal mode theory for coupled transmission lines. A new transfer matrix description
for a general optical directional coupler is presented. Based on this transfer matrix
formulation, the wavelength-dependent characteristics of multi-section optical filters
consisting of cascaded asymmetric optical directional coupler sections are investigated. It
is shown that by varying the asymmetry factors of the cascaded coupled waveguide
sections, optical wavelength filters with different passband properties can be achieved.
