The use of metal filled via holes for improving isolation in LTCCRF and wireless multichip packages

LTCC MCM's for RF and wireless systems often use metal filled via holes to improve isolation between the stripline and microstrip interconnects. In this paper, results from a 3D-FEM electromagnetic characterization of microstrip and stripline interconnects with metal filled via fences for isolation are presented. It is shown that placement of a via hole fence closer than three times the substrate height to the transmission lines increases radiation and coupling. Radiation loss and reflections are increased when a short via fence is used in areas suspected of having high radiation. Also, via posts should not be separated by more than three times the substrate height for low radiation loss, coupling, and suppression of higher order modes in a package     

Reliability of microwave SiGe/Si heterojunction bipolar transistors

The degradation behavior of NPN Si/SiGe/Si heterojunction bipolar transistors, grown by solid-source molecular beam epitaxy (MBE), has been studied by accelerated lifetime testing at different ambient temperatures. The degradations of the dc current gain and the microwave performance of the devices are explained in terms of recombination enhanced impurity diffusion (REID) of boron atoms from the base region and the subsequent formation of parasitic energy barriers at the base-emitter and base-collector junctions     

Crosstalk between finite ground coplanar waveguides over polyimide layers for 3-D MMICs on Si substrates

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 highand low-resistivity silicon wafers with a polyimide overlay. It is shown that a gap as small as 6 /spl mu/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).     

A theoretical and experimental study of coplanar waveguide shuntstubs

A comprehensive theoretical and experimental study of straight and bend coplanar waveguide (CPW) shunt stubs is presented. In the theoretical analysis, the CPW is assumed to be inside a cavity, while, the experiments are performed on open structures. For the analysis of CPW discontinuities with air-bridges, a hybrid technique has been developed which has been validated through extensive theoretical and experimental comparisons. Throughout this study, the effect of the cavity resonances on the behavior of the stubs with and without air-bridges is investigated. In addition, the encountered radiation loss due to the discontinuities is evaluated experimentally     

A measurement-based design equation for the attenuation ofMMIC-compatible coplanar waveguides

Measured attenuation of coplanar waveguide (CPW) transmission lines with narrow strip and slot widths fabricated on GaAs, high-resistivity Si, and InP is used to derive a new closed form equation to calculate line losses. This new equation is shown to be more accurate than previous expressions, yet simple enough to be programmed into a hand-held calculator since it is based on a simple relationship between attenuation and the product of the strip and slot widths. The derived equation is applicable to CPW's with aspect ratio and metal thicknesses commonly used in monolithic microwave integrated circuits     

Coupling between microstrip lines with finite width ground plane embedded in thin-film circuits

Three-dimensional (3-D) interconnects built upon multiple layers of polyimide are required for constructing 3-D circuits on CMOS (low resistivity) Si wafers, GaAs, and ceramic substrates. Thin-film microstrip lines (TFMS) with finite-width ground planes embedded in the polyimide are often used. However, the closely spaced TFMS fines are susceptible to high levels of coupling, which degrades the circuit performance. In this paper, finite-difference time domain (FDTD) analysis and experimental measurements are used to demonstrate that the ground planes must be connected by via holes to reduce coupling in both the forward and backward directions. Furthermore, it is shown that coupled microstrip lines establish a slotline type mode between the two ground planes and a dielectric waveguide type mode, and that the connected via holes recommended here eliminate these two modes.     

Design of layered ridge dielectric waveguide for millimeter and sub-millimeter wave circuits

Design rules for Layered Ridge Dielectric Waveguide (LRDW) are presented for the first time through simple figures and closed form equations. The Effective Dielectric Constant (EDC) method is used to develop the design rules that account for typical circuit specifications such as higher order mode suppression, dispersion, attenuation, and coupling between adjacent transmission lines. Comparisons between the design of LRDW, image guide, and millimeter-wave dielectric ridge guide are made.     

A comparative study between shielded and open coplanar waveguide discontinuities

A comparative study between open and shielded coplanar waveguide (CPW) discontinuities is presented. In this study, the space domain integral equation method is used to characterize several discontinuities such as the open-end CPW and CPW series stubs. Two different geometries of CPW series stubs (straight and bent stubs) are compared with respect to resonant frequency and radiation loss. In addition, the encountered radiation loss due to different CPW shunt stubs is evaluated experimentally. The notion of forced radiation simulation is presented, and the results of such a simulation are compared to the actual radiation loss obtained rigorously. It is shown that such a simulation cannot give reliable results concerning radiation loss from printed circuits.     

Finite ground coplanar waveguide (FGC) low loss, low coupling 90-degree crossover junctions

Microwave and millimeter-wave integrated circuits and RF distribution networks often require two transmission lines to cross over each other. In this paper, experimental measurements and three-dimensional (3-D) finite difference time domain analysis are used to thoroughly characterize coplanar waveguide (CPW) and finite ground coplanar waveguide (FGC) 90-degree crossover junctions. It is shown that FGC crossover junctions have approximately 15 dB lower coupling than CPW crossover junctions. Furthermore, it is shown that the FGC junctions do not excite the parasitic slotline mode, whereas, the CPW junctions do excite the slotline mode. The results presented indicate that the FGC crossover junction is easier to implement and has better characteristics than the CPW crossover junction.     

1-GHz, 200/spl deg/C, SiC MESFET Clapp oscillator

A SiC Clapp oscillator fabricated on an alumina substrate with chip capacitors and spiral inductors is designed for high-temperature operation at 1GHz. The oscillator operated from 30/spl deg/C to 200/spl deg/C with an output power of 21.8dBm at 1GHz and 200/spl deg/C. The efficiency at 200/spl deg/ C is 15%. The frequency variation over the temperature range is less than 0.5%.