Polyimide based GaAs micromachined millimeter wave structures

This paper presents the manufacturing of high-performance millimeter wave l umped elements on polyimide membranes obtained by micromachining of semi-in sulating GaAs. The microwave performances of the devices are compared with those obtained for similar structures manufactured on SiO2/Si3N4/SiO2 membr anes 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 t he substantial decrease in the parasitic capacitances and, as a result, the outstanding improvement in the resonant frequency of membrane supported in ductors. Comparative analysis of roughness and planarity of both types of m icromachined 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.