Coupling of high-overtone bulk acoustic resonators

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master_Tjepkema_Jonas_2025.pdf (17.44 MB)

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School of Science | Master's thesis
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Date

2025-09-29

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Major/Subject

Materials Physics and Quantum Technology

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Degree programme

Master's Programme in Engineering Physics

Language

en

Pages

147

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Abstract

The aim of this thesis is to investigate the coupling mechanisms of two AlN-Sapphire High-overtone Bulk Acoustic Resonators (HBARs) sharing the same substrate. The text combines the fundamentals of solid mechanics, piezoelectricity, analytical modelling of HBARs, finite-element simulations, and experimental measurements of fabricated samples. This strong theoretical basis hopes to construct a coherent body of work that simultaneously describes an understudied coupling pathway for HBARs, and can be used as a relevant reference/learning document on the field of acoustic resonators. Common frameworks, like the Butterworth-Van Dyke model and Mason's model, are built and modified with the goal of developing a novel 1D simulation method for this laterally coupled HBAR system. These numerical results are then contrasted to different finite element simulations of the system. An in-depth description of the design and material choices is given, as well as the complete fabrication processes combined to a commentary on the successes and failures of the procedures and resulting samples. The subsequent sample measurements revealed that only a subset of fabricated devices exhibited relatively clear evidence of coupling, characterized by splitting of resonance dips and periodic mode behaviour which were consistent with some computed predictions. In particular, three samples showed strong signatures/indications of mutual coupling, while others remained inconclusive but hinted at weaker forms of interactions.

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Supervisor

Sillanpää, Mika

Thesis advisor

Wu, Longhao

Keywords

acoustic resonators, acoustic waves, HBAR, phonons, coupling, low temperature physics

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https://urn.fi/URN:NBN:fi:aalto-202510228518

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[dipl] Perustieteiden korkeakoulu / SCI