Micromachined Interfaces for Metrology and Packaging Applications in the Submillimeter-Wave Band

The continued emergence of new terahertz devices has created a need for improved approaches to packaging, integration, and measurement tools for diagnostics and characterization in this portion of the spectrum. Rectangular waveguide has for many years been the primary transmission medium for terahertz and submillimeter-wave systems operating from 300 GHz to 1 THz, with the UG-387 flange the most common interface for mating waveguide components over this frequency range. Alignment of UG-387 flanges is accomplished with pins and alignment holes that are placed around the flange perimeter and, under the standard MIL SPECS tolerances, misalignments of up to 6 mils (150 microns) are possible as a result of practical milling tolerances. With the emergence of vector network analyzers operating beyond 1 THz, such misalignment of waveguide mating flanges is not negligible and is recognized as a fundamental issue limiting calibration and measurement precision at frequencies greater than 300 GHz. In response to this issue, a number of new waveguide flange concepts have been investigated to reduce flange misalignment and the P1785 IEEE Standard was recently issued to recommend designs for waveguide interfaces at frequencies above 110 GHz. Among the new flange concepts being proposed is a modified UG-387 that utilizes tighter machining tolerances and the ring-centered flange where alignment is accomplished using a precision coupling ring that fits over raised bosses that are centered on each waveguide. This paper discusses the new interface concepts that are being developed to address waveguide flange misalignment as well as emerging micromachined interconnects, calibration standards and heterogeneous integration methods that are being applied to implement low-loss and high-performance circuit architectures for the terahertz frequency range. Among the technologies that will be described are (1) design and characterization methods for the new ring-centered waveguide standard, (2) micromachined waveguide components and calibration standards for the terahertz band, (3) silicon-based micromachined probe structures for direct-contact interfacing and metrology, and (4) epitaxial transfer of III-V semiconductor material onto high-resistivity silicon to realize a low-loss platform for integration of terahertz components. Details of the processing methods used to realize these components as well as measurement techniques for assessing their performance will be described.