Design and characterization of CPW feedthroughs in multi-layer thin-film MCM-D

We report on the design and characterization of CPW feedthroughs for RF and microwave applications in multi-layer thin-film MCM-D. Using 3-D simulations, it is shown that, for analysis purposes, the vertical metal wall, can be replaced with a thin (5 μm) metal layer with only a small impact on the actual performance. This equivalent structure can be more easily fabricated as the thin metal layer on the top is directly available in the multi-layer technology. This allows for a faster design and characterization of the feedthrough. The transmission line properties (characteristic impedance and propagation constant) of the intrinsic feedthrough are extracted based on the measurement of two equivalent lines with different length. Measurements indicate that a low-loss (<0.4 dB), well matched feedthrough (return loss below -25 dB) can be realized up to at least 50 GHz (intrinsic feedthrough length of 500 μm)