Coupling between microstrip lines embedded in polyimide layers for 3D-MMICs on Si

Three-dimensional circuits built on multiple layers of polyimide are required for constructing Si/SiGe monolithic microwave/millimetre-wave integrated circuits on CMOS (low resistivity) Si wafers. However, the closely spaced transmission lines are susceptible to high levels of coupling, which degrade circuit performance. In this paper, finite difference time domain (FDTD) analysis and measured characteristics of novel shielding structures that significantly reduce coupling between embedded microstrip lines are presented. A discussion of the electric and magnetic field distributions for the coupled microstrip lines is presented to provide a physical rationale for the presented results.