Micromachined high-frequency transmission lines on thin dielectric membranes.

This thesis represents a detailed investigation of high-frequency transmission lines which are supported by thin-film dielectric membranes. The associated fabrication techniques rely on established silicon micromachining technology to realize new architectures for high-performance microwave and millimeter wave circuits. In the majority of the material, attention is directed towards the characterization, fabrication, and measurement of a transmission line which has been named the microshield line. This is a quasi-planar geometry with a signal line and ground planes which are patterned on the thin membrane, and a lower shielding cavity which is realized by micromachining the silicon substrate. It is demonstrated that the microshield line offers significant advantages in comparison to conventional planar lines such as coplanar waveguide (CPW), in terms of attenuation, parasitic radiation, broadband operation, and overall circuit performance. Two of the chapters in the thesis are devoted to theoretical characterization of coplanar waveguide-type discontinuities, such as the microshield configuration. One method is a full-wave integral equation technique which has been used to analyze many of the circuits and antennas involved in this research. A more computationally efficient, but much less general, quasi-TEM analysis of coupled slot configurations is also presented. This method was developed in order to characterize new filter arrangements which combine distributed element tuning stubs with lumped element overlay capacitors. After describing the theoretical foundation, specific applications of the membrane-supported lines are considered. This includes several millimeter wave components such as transitions to conventional CPW, new geometries for compact tuning stubs, low-pass and band-pass filters, and the distributed/lumped element configurations mentioned above. To demonstrate the potential for high-performance submillimeter wave microshield circuits, the design, measurement, and performance of a 250 GHz planar bandpass filter are presented. A membrane-supported microstrip geometry is also investigated in order to realize a very low loss, Ka-band Wilkinson power divider/combiner. Finally, a study of new CPW-fed, single and double folded-slot antennas is described. These uniplanar designs exhibit very wide impedance bandwidths and well-shaped beam patterns. The thesis concludes by discussing some possible future directions for this work. Included in the appendices are general guidelines on the fabrication process used in this research and on the measurement of microshield circuits.Ph.D.Applied SciencesElectrical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/129738/2/9610262.pd