Sub-Terahertz Components and Systems Enabled by Silicon-micromachined Waveguide Circuits

Abstract

Sub-terahertz (Sub-THz) and THz spectrums are being used increasinglydue to the short wavelength and wide available bandwidthat these ranges. These spectrums hold significant importance in scientificand commercial applications such as detection, ranging, imaging,security screening, car radars for passenger monitoring and autonomousdriving, telecommunication, sensing, spectroscopy, and deep space exploration.However, implementing components and circuits in thesespectrums has many challenges due to high fabrication tolerance requirements.Therefore, there is a need to surpass conventional fabricationtechniques like computer-numerical-control (CNC) milling to fullyexploit the vast potential of these spectrums.

Silicon micromachined waveguides, realized by deep-reactive-ionetching(DRIE) of silicon-on-insulator (SOI) wafers and sidewall metallization,have been used to implement different components in this thesis.Silicon micromachining offers several advantages compared to otherfabrication techniques, such as micrometer range accuracy, smaller andlighter devices, nanometer range surface roughness leading to low insertionloss, integrability of active and passive components on a single chip,low cost, and volume manufacturability. This thesis presents severalnovel sub-THz components and systems that are composed of multipleelements, all designed to be implemented by silicon micromachining.

The thesis is structured as follows. After a short introduction, thefirst part of the thesis provides a detailed overview of the fabricationtechnology and presents a step-by-step fabrication process flow thatincludes various processes. This section also covers the challenges andlimitations of silicon micromachining and the strategies for addressingthem.

The second part of the thesis focuses on designing and characterizingdifferent silicon micromachined passive waveguide components, such asa full-band E-plane waveguide transition from reduced-height in-planewaveguides embedded inside the silicon substrate to standard out-ofplanewaveguide sizes, a rectangular waveguide-based magic-T, and adual-port dual-line 2 × 8 antenna array with frequency beam steering.The characterization procedure for every component is presented thoroughly,and the measured results are discussed shortly, as the resultsare already published in detail in the appended publications (Papers I,II, and III).

The third part of the thesis elaborates on MEMS-based waveguideswitches (Papers IV and V). This part explains the design and characterizationof a novel single-pole-single-throw (SPST) switch operatingin the 220-290 GHz frequency range with excellent insertion loss and isolation performance. The SPST switch is then integrated into a morecomplex signal chain and combined with hybrid couplers to create anovel crossover switching circuit. The designed crossover switch operatesin the 220-260 GHz frequency range with excellent insertion loss,return loss, and isolation, making it well-suited for receiver calibrationapplications. Additionally, the designed crossover switch is fullysymmetric regarding input-output signal paths, making it suitable forapplications with redundancy requirements.

Finally, the last part of the thesis presents a complex reconfigurablecar radar frontend circuit (Papers VI and VII). Several componentsare integrated into this signal chain with a compact footprint of only20mm × 14mm × 1.2mm. The designed radar frontend features frequencybeam steering and beam shape switching between a broad anda notched radiation pattern. It operates in the 220-260 GHz frequencyrange with a beam steering range of 238-248 GHz. The features of thedesigned radar frontend make it well-suited for target detection, ranging,and imaging applications.

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