This paper presents the fabrication processes for micromachined millimetre-wave devices, on two different types of semiconductor substrates. The first process uses micromachining on high-resistivity 100 oriented silicon. A three-layer dielectric membrane, with a total thickness of 1.5 µm is used as support for the millimetre-wave structures. This process was used for the manufacturing of two coupled line filters, with central operating frequencies of 38 and 77 GHz, respectively. The second process is based on GaAs micromachining. For the first time, a 2.2 µm thin GaAs/AlGaAs membrane, obtained by molecular beam epitaxy growth and micromachining of semi-insulating 100 GaAs, is used as a support for millimetre-wave filter structures. Cascaded coplanar waveguide open-end series stubs filter type structures, with central frequencies of 38 and 77 GHz, respectively, were designed and manufactured on a GaAs micromachined substrate. 'On wafer' measurements for the filter structures were performed. Losses of less than 1.5 dB at 38 GHz and less than 2 dB at 77 GHz have been obtained for both the silicon as well as for the GaAs-based micromachined filters.

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 SiO2/Si3N4/SiO2 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 membrane 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.

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A GaAs micromachined uniplanar quasi-optical mixer is presented for the first time. The main block of the circuit is a membrane-supported double folded slot antenna monolithically integrated with a millimeter-wave Schottky diode. The circuit is designed for the 38 GHz frequency range, using coplanar waveguide technology and full-wave electromagnetic simulations, and is fabricated on a large GaAs membrane. The mixer is characterized using the isotropic conversion losses parameter and a value of 16 dB was measured

This paper presents the design and fabrication of micromachined GaAs membrane supported millimeter-wave passive circuits. A new type of coupled line band-pass filter demonstrator structure for millimeter-wave applications was designed and fabricated on a 2.2 µm thick GaAs membrane. Low insertion losses were demonstrated. Also, GaAs membrane supported Yagi–Uda antenna structures for applications in the millimeter-wave frequency range were designed and manufactured. The technological approach allows the fabrication of three-edge membranes, which support the antenna structures. This topology assures optimum radiation conditions for these endfire-type antennae. The characterization of a 45 GHz and a 60 GHz antenna structure validates the technological approach.