Advancing GaN MMIC technology through fabrication technique enhancement

Collier, Arthur 2024. Advancing GaN MMIC technology through fabrication technique enhancement. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis advances gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) technology by optimising fabrication processes, integrating innovative manufacturing techniques, and comprehensively characterising material and device performance to provide feedback on design and fabrication alterations. The research addresses critical challenges in MMIC design, including current collapse, linearity, and limitations of conventional fabrication methods, with a focus on both microwave and mm-wave applications. Key contributions include the development of a localised electrodeposition metal additive micro-manufacturing (LEDμAM) process, enabling the fabrication of advanced air-bridge structures and the introduction of cavity coplanar waveguides (CCPW). These innovations improve impedance matching while suppressing parasitic modes, as demonstrated through simulations and measurements. The thesis also provides an in-depth evaluation of amorphous silicon nitride (SiNx) stoichiometry, correlating material properties such as refractive index and hydrogen content with electrical performance. Tailored SiNx recipes are proposed for MMIC passivation and capacitor applications, validated through experimental characterisation and modeling. Isolation methods for GaN-on-Si HEMT switches were comprehensively compared, with ion implantation and mesa etching evaluated in terms of RF and large-signal performance. The analysis revealed key trade-offs, such as improved DC leakage in ion-implanted devices versus greater power handling capabilities for mesa-etched designs, guiding optimisation strategies for high-frequency MMIC applications. Collectively, these findings contribute to the state-of-the-art in GaN MMIC technology, demonstrating pathways to more efficient and reliable devices. The outcomes of this work provide a foundation for advancing GaN MMIC fabrication techniques to meet the demands of next-generation high-frequency applications.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. Gallium nitride 2. High electron mobility transistor 3. Monolithic microwave integrated circuits 4. Localised electrodeposition 5. Silicon nitride 6. Isolation
Date of First Compliant Deposit:	21 July 2025
Last Modified:	21 Jul 2025 09:01
URI:	https://orca.cardiff.ac.uk/id/eprint/179917

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