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Abstract--Three-dimenslonal circuits built upon multiple layers of polyimide are required for constructing Si/SiGe monolithic microwave/millimeter-wave integrated circuits on CMOS (low resistivity) Si wafers. Thin film microstrip lines (TFMS) with finite width ground planes embedded in the polyimide are often used. However, the closely spaced TFMS lines are susceptible to high levels of coupling, which degrades circuit performance. In this paper, Finite Difference Time Domain (FDTD) analysis and experimental measurements are used to show that the ground planes must be connected by via holes to reduce coupling in both the forward and backward directions,

Abstract--Three-dimensional (3D) interconnects built upon multiple layers of polyimide are required for constructing 3D circuits On CMOS (low r esistivity) Si wafers, GaAs, and cera mic substrates. Thin film micros trip lines (TFMS) with finite width ground planes embedded in the polyimide are often used. However, the closely spaced TFMS lines are susceptible to high levels of coupI.ing, which degrades circuit performance. In this paper, Finite Difference T ime Domain (FDTD) analys is and experimental measurements are used to show that the ground planes must be connected by via holes to r ed uce coupling in both the forward and backward directions.Furthermore, it is shown that coupled micros trip lines establish a slotline type mode between the two gro und planes and a dielectric waveguide type mode, and that the via holes recommended her e eliminate these two modes.

Measured propagation characteristicsof Finite Ground Coplanar (FGC) waveguide on silicon substrates with resistivities spanning 3 orders of magnitude (0.1 to 15.5 Ohm cm) and a 20 I.tm thick polyimide interface layer is presented as a function of the FGC geometry. Results show that there is an optimum FGC geometry for minimum loss, and silicon with a resistivity of 0.1 Ohm cm has greater loss than substrates with higher and lower resistivity. Lastly, substrates with a resistivity of 10 Ohm cm or greater have acceptable loss.

Abstract-Finite-ground coplanar (FGC) waveguide lines on top of polyimide layers are frequently used to construct three-dimensional Si-SiGe monolithic microwave/millimeter-wave integrated circuits on silicon substrates. Requirements for high-density, low-cost, and compact RF front ends on silicon can lead, however, to high crosstalk between FGC lines and overall circuit performance degradation. This paper presents theoretical and experimental results and associated design guidelines for FGC line coupling on both high-and low-resistivity silicon wafers with a polyimide overlay. It is shown that a gap as small as 6 m between two adjacent FGC lines can reduce crosstalk by at least 10 dB, that the nature of the coupling mechanism is not the same as with microstrip lines on polyimide layers, and that the coupling is not dependent on the Si resistivity. With careful layout design, isolation values of better than 30 dB can be achieved up to very high frequencies (50 GHz).Index Terms-Coplanar waveguide (CPW), coupling, crosstalk, finite difference time domain (FDTD), finite ground coplanar (FGC) waveguide, monolithic microwave integrated circuit (MMIC), polyimide.