Low-Loss Microcoax-to-CPW Transition for Air-gapped Microcoaxial Passives

This letter presents the detailed design and characterization of microcoax-to-coplanar waveguide (CPW) transition for air-gapped microcoaxial passives. The microcoax-to-CPW transition is fabricated by multilayer Cu Damescene process with a low thermal budget and fully compatible with CMOS back-end-of-line (BEOL) process. The fabricated microcoax-to-CPW transition has demonstrated an insertion loss less than 0.25 dB and return loss better than 30 dB in frequency range from 0.1 to 40 GHz. The characteristic impedance (Z0) of the microcoax-to-CPW transition is well matched to 50 Ω. The low loss transition can serve as the essential interface for integration of microcoaxial passives with the conventional monolithic microwave integrated circuits (MMICs).