Polyimide based GaAs micromachined millimeter wave structures

This paper presents the manufacturing of high-performance millimeter wave lumped elements on polyimide membranes obtained by micromachining of semi-insulating GaAs. The microwave performances of the devices are compared with those obtained for similar structures manufactured on SiO sub(2)/Si sub(3)N sub(4)/SiO sub(2) membranes on silicon micromachined substrates, as well as with the performances of similar devices manufactured on bulk GaAs and high-resistivity silicon. S parameter analysis and the computed lumped equivalent circuit emphasize the substantial decrease in the parasitic capacitances and, as a result, the outstanding improvement in the resonant frequency of membranes supported inductors. Comparative analysis of roughness and planarity of both types of micromachined structures was also performed. Polyimide membranes manufactured on GaAs substrate have proved to be a very good support for millimeter wave circuit elements, both from mechanical as well as electrical points of view.