A Technology of Thin-Film Hybrid Microwave Circuits

This paper describes the various thin-film processes that are being used to produce microwave integrated circuits, both microstrip and lumped element systems. The technologies described involve a combination of vacuum evaporation or RF sputtering, photolithographic, electrochemical, and microbonding processes used in sequence to achieve integrated resistor, capacitor, and conductor networks. Stable thin-film integrated nickel-chromium resistors are achieved with good microwave behavior. The usual conductor and interdigital capacitor systems are gold with either nickel-chromium or titanium underlay. The microwave circuits are produced on a variety of substrates which include alumina, ferrite, quartz, and sapphire. Some of the ancillary amplifier networks are produced on glass, A successful scheme for the fabrication of integrated anodized aluminium capacitor structures, compatible with the nickel-chromium/gold resistor conductor system, is outlined as well as preliminary results of such systems at GHz frequencies. Assembly techniques used for incorporating add-on components including chip capacitors, overlay couplers, chip resistors, and microwave semiconductor devices are included. Substrate preparation and the packaging of prototype assemblies are also included. Examples are shown of components and systems where the various technologies have been successfully applied. Data on the manufactured components are given, showing that good reliable performance can be achieved. While the processes are typically operated in the environment of a workshop for circuit development, they are adaptable for large-scale manufacture.