3-D low-loss coplanar waveguide transmission lines in multilayer MMICs

Newly developed transmission-line structures using the great flexibility of three-dimensional multilayer technology have been designed and fabricated. In this paper, we demonstrate that monolithic microwave integrated circuit (MMIC) coplanar waveguide transmission lines with a wide range of characteristic impedances can easily be designed using the multilayer technique. Furthermore, this implementation can avoid the well-known current crowding effects on the conductor edges minimizing dissipation loss. The system of three layers of metals and two layers of sandwich polyimide as dielectrics was employed. The fabricated transmission lines have been characterized providing a wide range of impedances from 10 to 70 Omega. In addition, the effects of unintentional horizontal and vertical coupling in multilayer MMICs have been investigated. The results indicated that an optimum separation of 75 mum is necessary for negligible coupling (~-30 dB)