Characterization of vertical interconnects in three-dimensional monolithic microwave integrated circuits (three-dimensional MMIC)

In this research, a unique fabrication technology to build high-aspect-ratio via interconnects in 3D MMIC multilayer integration was developed from a combination of microelectronic and traditional MEMS microfabrication technologies. Based on these techniques, a set of test structures have been successfully fabricated to facilitate the vertical interconnect characterization.; Fully cured polyimide thin films possess favorable electric and mechanical properties for the 3D MMIC applications. Using quarter wavelength T-junction resonator structure, polyimide was characterized for its microwave properties. High-frequency characterization of polyimide thin films was obtained in a wide frequency range. Experimental results have shown the feasibility of this method.; In order to correctly evaluate the conductor loss in thin planar transmission lines, a modified conductor loss model was derived from conventional Wheeler's incremental inductance rule to account for the field penetration as the physical strip thickness approaches the skin depth or even smaller. The closed-form formulas or simplified equations have been developed for microstrip and stripline with wide strip cases, and for general coplanar waveguide including SCPWG line. Meanwhile, experimental results verified the validity of the modified conductor loss model in evaluating the losses in thin transmission lines. It has been shown that as the conductor thickness becomes approximately greater than four times of the skin depth, both conventional Wheeler's rule and its modified model agree with each other very well on the conductor loss estimation.; Experimental results have revealed that at RF frequency, e.g. X band (8–12 GHz), the vertical interconnection discontinuities may contribute significantly to the insertion loss and the phase change. With the advanced conductor loss models for evaluating the characteristics in the test structures, lumped-element equivalent circuit models can be derived from the via module measurement results. These models are of great practical importance in a complex circuit design.