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Exploiting the Terahertz Spectrum with Silicon Micromachining

Waveguide Components, Systems and Metrology

Time: Mon 2021-03-29 14.00

Location: or online defense (English)

Subject area: Electrical Engineering

Doctoral student: James Campion , Mikro- och nanosystemteknik

Opponent: Professor Robert M. Weikle II, University of Virginia, Charlottesville, Virginia, USA

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


The terahertz spectrum (300 GHz - 3 THz) represents the final frontier for modern electronic and optical systems, wherein few low-cost, volume-manufacturable solutions exist. THz frequencies are of great scientific and commercial interest, with applications as diverse as radio astronomy, sensing and imaging and wireless communications. Current THz technology is restricted by its expense, form-factor and performance limitations. Future exploitation of this spectrum requires the development of new technologies which support its use in high-volume applications. Any such technology must offer excellent mechanical and electrical performance and be compatible with industrial grade tools and processes. In response to this, this thesis presents the development of silicon micromachined waveguide components and systems for THz and sub-THz frequencies. Silicon micromachining offers a unique combination of small feature sizes and low surface roughness and manufacturing tolerances in a scalable process.

At the core of this work lies a new silicon-on-insulator (SOI) waveguide technology which minimises surface roughness to provide low insertion loss. Waveguide filters and diplexers between 100–500 GHz are implemented using this technology, each with state-of-the-art performance. A new platform for waveguide systems is developed to enable fully micromachined systems to be realised. In contrast to previous solutions, this platform integrates of all DC, intermediate and radio frequency signals in a single medium. Two unique non-galvanic transitions provide interfaces to active components and metallic waveguides. Semi-automated industrial tools perform system assembly with high accuracy and are used to implement complete transceivers for wireless communication at 110–170 GHz. Commercial-grade silicon germanium integrated circuits are used for all active components. This represents the first step in the adoption of this new technology in an industrial scenario.

Large-scale use of the THz spectrum necessitates a shift from discrete components to complete integrated systems, in a similar matter to that seen in digital electronics and will require accurate, high-throughput characterisation and verification infrastructures. To support this, two transitions from co-planar waveguide probes to rectangular waveguide are proposed to allow for device characterisation in an on-wafer environment from 220–500 GHz. The accuracy and precision of the SOI micromachining process, coupled with the mechanical properties of silicon, make it highly suited to the creation of precision metrology standards. By harnessing these properties, a new class of micromachined waveguide calibration standards is developed, the peformance of which exceeds current solutions. Traceability of the standards is documented through detailed mechanical, electrical and statistcal analysis of fabricated samples.

This work presented in thesis enables the development of THz components and systems, and methods to test them, in an established, high-volume technology, enabling their use in a wide range of applications.