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Silicon micromachined waveguide components for terahertz systems

Time: Tue 2020-11-24 14.00

Location:, Stockholm (English)

Subject area: Electrical Engineering

Doctoral student: Bernhard Beuerle , Mikro- och nanosystemteknik

Opponent: Professor Kamal Sarabandi, University of Michigan

Supervisor: Professor Joachim Oberhammer, Mikro- och nanosystemteknik; Umer Shah, Mikro- och nanosystemteknik

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This thesis presents silicon micromachined waveguide components for sub-terahertz and terahertz (THz) systems fabricated by deep reactive ion etching (DRIE). Historically the main driving force for the development of THz systems has been space-based scientific instruments for astrophysics, planetary and Earth science missions. Recent advances in active and passive components for the THz frequency range increased its usage in areas such as imaging, security, communications and biological instrumentation. Traditionally the primary technology for components and interconnections approaching THz frequencies has been hollow metal waveguides fabricated by computer numerical controlled (CNC) milling. Systems using this technology are bulky and hand-assembled, getting more expensive and complicated with an increasing complexity of the system. In recent years silicon micromachining has emerged as a viable alternative for THz components and integrated systems promising more compact integrated systems.The thesis reports on a new low-loss silicon micromachined waveguide technology using silion-on-insulator (SOI) wafers. Several low-loss waveguide components in the frequency range of 220–330 GHz have been fabricated and characterized, such as hybrid couplers, splitters and matched loads. Furthermore, an investigation of fabrication accuracy and repeatability for high-Q filters in the sub-THz frequency range using the same waveguide technology is presented.For on-wafer waveguide characterization a novel CPW probe to micromachined waveguide transition concept is introduced. The transition is co-fabricated together with the devices under test in the same waveguide technology using SOI technology. It consists of a CPW probing interface and a pin protruding into the waveguide cavity acting as an E-field probe to excite the dominant mode of the rectangular waveguide. Designed and characterized for the frequency range of 220–330 GHz, the transition was successfully used for on-wafer characterization of the waveguide components previously presented. The scalability of the concept to higher frequencies is shown by presenting a modified transition capable of device characterization up to 500 GHz.The integration of monolithic micromachined integrated circuits (MMICs) with silicon micromachined waveguides is investigated, with a focus on scalability to higher frequencies and their compatibility with industrial assembly tools. A new integration concept for THz systems is presented and a back-to-back transition structure for the integration of SiGe MMICs with silicon micromachined waveguides at D-band frequencies (110–170 GHz) has been characterized. Furthermore, a co-designed transition from InP MMIC to silicon micromachined rectangular waveguide is presented, consisting of a compact microstrip to waveguide transition and a vertical waveguide to in-plane waveguide bend in the silicon micromachined waveguide technology. The concept has been fabricated and characterized in a back-to-back configuration for the frequency range of 220–330 GHz.