Super-high-frequency lithium niobate microelectromechanical system resonators
Recently, the rapid growth of super-high-frequency (SHF) applications has fueled the development of wideband filters and multiplexers. To achieve the desired performance, the building blocks of these filters, namely the acoustic resonators, must feature resonances at SHF, and high figure of merit (FOM) for minimal insertion loss and enhanced out-of-band rejection. This thesis reports on the demonstration of a new class of SHF microelectromechanical system (MEMS) resonators operating in the 5 GHz range. The SHF resonances have been achieved by employing the first order antisymmetric (A1) mode in ion-sliced and suspended Z-cut lithium niobate (LiNbO3) thin films, which feature a phase velocity exceeding 10,000 m/s. The fabricated device has demonstrated a high electromechanical coupling (kt2) of 29% and a high quality factor (Q) of 527 simultaneously. Hence, this work marks the first time that MEMS resonators at SHF were demonstrated with an extremely high figure of merit (FoM= kt2Q) of 153. The SHF operation and high FoM of these A1 mode devices have proven their potential as the key building blocks for future SHF front-end filters and multiplexers. This thesis is organized as follows. In Chapter 1, the background of RF-MEMS filters and resonators will be reviewed and the motivation of developing SHF MEMS resonators is clarified. Chapter 2 will introduce fundamentals and materials of piezoelectric MEMS resonators. Chapter 3 will discuss characteristics of Lamb wave modes and detail the first-order antisymmetric (A1) Lamb wave mode which can be employed in designs of SHF LiNbO3 MEMS resonators. Chapter 4 will present and describe the microfabrication process of the SHF LiNbO3 MEMS resonators. Finally, Chapter 5 will conclude this research work and suggest some potential future research directions.
Super-high-frequency, Microelectromechanical system (MEMS), Lithium niobate, Resonator
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign