Coplanar waveguide structures on micromachined glass substrates

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Bugyik, Paul L.
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Micromachining is currently being studied to help reduce the packaging and integration costs of multi-chip modules (MCMs) in radio frequency (RF) systems. Such systems require the integration of radiating elements, feed networks, micro-electromechanical systems (MEMS), and monolithic microwave integrated circuits (MMICs). Each subsystem has its own requirements in terms of material properties. Antennas radiate best when located on low dielectric constant materials, while higher dielectric constant materials permit smaller size for feed networks. In both cases low loss is a practical concern. Ideally one material could be used which would satisfy all the requirements. In this work a sequence of processes to create thick copper coplanar waveguide (CPW) structures on low-cost aluminosilicate glass substrates is proposed and demonstrated. Conductor loss as a function of geometry and conductor thickness will be discussed. Results will be presented that indicate the effective dielectric constant of a single substrate material can be varied by micromachining an air/dielectric lattice structure beneath perforated conductors. This micromachined perforated CPW (MCPW) structure can effectively provide multiple dielectrics with a single material. The micromachined structures are characterized against a regular finite ground CPW and compared against numerical predictions.