TABLE OF CONTENTS The fabrication of microwave integrated circuits needs knowledge, skill, and experience in standard photolithography and chemical etching techniques [1]. Regarding widely used hybrid technology, this includes preparation of the mask of the circuit layout, cleaning the substrate surface, covering the surface with photo resist, and illuminating it with the mask attached. After exposure, the photo resist is developed, and the substrate etched and cleaned. Then, if needed, lumped elements are placed onto the circuit. Finally, for practical usage, the complete circuit is mounted in a package with microstrip-to-coaxial adapters and feedthroughs for the bias leads.
The photolithographic process for the realization of microstrip circuits has been widely discussed in the literature (e.g., [1 7]), so that the basic processing steps do not need to be described further. Nevertheless, technology has to be developed given specific conditions and specifications with respect to substrate materials, instruments, and chemicals. To specify the various process parameters, partially extensive test runs have to be performed. Process-related underetching effects or attainable minimum width of a microstrip line are important design constraints. Especially with coupled line circuits, underetching may be significant [8].
There exists a wide range of substrate materials with various material parameters. With respect to easy mechanical processing, soft plastic substrates are frequently prefered to rigid hard substrates, such as alumina or, in special cases, ferrite materials. Soft materials have advantages in grounding devices by cutting or drilling holes through the substrate and shortening by conductive copper foil. In a similar way, short-circuited...
