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Advanced MEMS Technology for Terahertz Frequencies

Time: Fri 2021-04-16 10.00

Location: zoom link for online defense (English)

Subject area: Electrical Engineering

Doctoral student: Zhao Xinghai , Mikro- och nanosystemteknik

Opponent: Professor Jan Stake, Chalmers University of Technology

Supervisor: Professor Joachim Oberhammer, Mikro- och nanosystemteknik; Dr. Umer Shah, Mikro- och nanosystemteknik; Dr. Oleksandr Glubokov, Mikro- och nanosystemteknik

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With the development of terahertz (THz) technology, a variety of application demands are growing rapidly, such as high-rate communications, THz radars, environmental monitoring, medical imaging, and space exploration. However, the fabrication, integration, and packaging techniques for THz components and systems pose great challenges for a large-scale, cost-effective production. The current THz technology relies on the conventional and expensive serial fabrication and packaging techniques, such as computer numerical control (CNC) high-precision machining, which are suitable only for high-end research instrumentation or one-off prototypes. Nowadays, THz microelectromechanical system (MEMS) is a leading candidate to realize high-precision, low-cost, large-volume fabrication, and integration for miniaturized THz components and systems. In this thesis, several key components and technologies of THz MEMS are developed towards the progression of future THz microsystem front-ends.

In the following research, D-band filters and diplexers have been implemented by an advanced Si micromachining technology based on a releasable-filling-structure (RFS) approach which can achieve high-precision geometries for THz waveguide devices. Fabrication imperfection is a big issue which affects the performance of the devices, namely, insertion loss, bandwidth, and operation frequency. The RFS-based silicon-on-insulator (SOI) micromachining technology improves the deep reactive ion etching (DRIE) processing performance, especially sidewall verticality, by utilizing extra structures to fill the large areas, which in turn, can obtain uniform etching aspect ratios.

The state-of-the-art MEMS phase shifter based on a waveguide-integrated SOI micromachining technology has been successfully demonstrated at 220-330 GHz, with a full-band and low insertion-loss characterization. MEMS comb-drive actuators are integrated in the device layer of the SOI substrate, which move Si slabs in a rectangular waveguide of the handle layer for changing the propagation constant. Integrating tunability or reconfigurability into THz microsystems is a very crucial aspect for implementing signal modulation, frequency band selection, beam scanning, and calibration applications in THz MEMS front-ends. The demonstrated work paves the way towards a three-dimensional (3D)-micromachined, SOI integrated rectangular waveguide microsystem.

A series of high-Q multilayer filters have been achieved by a vertically stacked Si-chip micromachining technology. The frequencies cover 270 GHz, 300 GHz, 450 GHz, 687 GHz and 700 GHz. The fabrication accuracy and repeatability of this kind of THz waveguide filters based on this vertically stacked multilayer platform have been investigated by experiments. A versatile axial-port-integrated multilayer device concept has been proposed for enabling the direct on-flange characterization and integration for advanced THz waveguide components. H-plane waveguide filters with versatile axial-interfaces based on the vertically stacked multilayer platform has been successfully demonstrated. This vertically stacked multilayer Si micromachining technology shows a promising potential in implementing highly integrated, compact 3D THz microsystems.