Glass Air-Gap Transmission Lines on Silicon for Microwave Integrate Circuits

Two types of air-gap transmission-line structures on silicon substrates have been fabricated using glass microbump bonding (GMBB) techniques. The air-gap transmission lines have the advantages of lower losses compare to conventional uniplanar transmission-line on doped semiconductor substrate. Because the bonding techniques are simple, this integration approach provides a cost-effective solution for monolithic microwave integrated circuits (MMICs). Theoretical and experimental results of air-gap interconnects on silicon substrate are presented in this paper. Spiral inductors fabricated in air-gap configurations are also experimentally studied. The temperature effects on losses are investigated as well.