Terahertz Micromachined Resonator Superstructures

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This application has three distinct but interrelated research areas. The first is a method of designing microwave circuits using inter-coupled resonators. The method is extremely general, and can be used over a wide frequency range with many different technologies used in microwave circuits. The second area is using micromachined terahertz devices to exemplify the new deign techniques at a particular frequency and for a particular application. Micromachining has to be used to make accurate dimensioned waveguides with accuracies down to microns. The third area is the improvement in the micromachining process for the terahertz application.Inter-coupled resonators have been used for many years to make microwave filters. For more complex passpand responses with transmission zeros or dual bands, the inter-coupling becomes much more complex. This proposal takes this concept a stage further and proposes that whole passive systems can be made using coupled resonators or resonator superstructures. To exemplify this the authors have already demonstrated power splitters and a diplexers based on these concepts, and the proposed work is to look at antenna feed networks, Butler matrices and filter banks. The techniques can provide the design of microwave circuits at any centre frequency and will be useful in many areas. Technology is now allowing systems to be constructed at much higher frequencies; mobile communications at around 2 GHz is now commonplace, but car radar systems at 77 GHz have only just developed in the last few years, and now applications are beginning to emerge at above 100 GHz in the submillimetre wave region. Applications to 1 terahertz and above are seen as extremely important for future systems. One of the lowest loss waveguide structures is the rectangular waveguide, and this work will look at micromachined waveguide. The circuits are made by stacking layers of metalised silicon or thick resists. Two of the layers act as the top and bottom of the guide and the interleaving layer (or layers) forms the walls of the hollow rectangular tube. For 300GHz these waveguide are about 800 by 400 microns and micromachining is therefore required to make them accurately at this size. At Birmingham a reliable, accurate techniques for bonding the layers has been developed. Structures such as filters, power splitters, diplexers and triplexers will be demonstrated. The resonator superstructures will be also configured in waveguide resonators to produce submillimetre wave antenna feed networks, Butler matrices and filter banks.Finally work will be done to improve the micromachining process. This includes being able to selectively pattern the top and vertical edges of the gold coating. This will enable transitions to other transmissions structures such as coplanar waveguides as well as the ability to improve the bonding between layers. In addition work will proceed on the development of a new dielectric waveguide structure, initially looking at the embedding of quartz nano particles in the resist SU8. Providing a low loss waveguide structure will give the microwave designer another tool for circuit construction.