Optimization and design of radio frequency piezoelectric MEMS resonators

Radio frequency (RF) microelectromechanical system (MEMS) resonators employing Lamb waves propagating in piezoelectric thin films have recently attracted much attention since they combine the advantages of the bulk acoustic wave (BAW) and surface acoustic wave (SAW) technologies: high phase velocity and multiple frequencies on a single chip. In particular, aluminum nitride (AlN) resonators based on fundamental symmetric (S0) Lamb mode have shown great promise because they can offer high phase velocities (10,000 m/s), low dispersive phase velocity characteristic, small temperature-induced frequency drift, low motional resistance, and monolithic integration compatibility with complementary metal–oxide–semiconductor (CMOS). However, there are still a few outstanding technical challenges, including spurious modes suppression, quality factor (Q) enhancement, frequency scalability, and electromechanical coupling improvement. These issues obstruct the wide deployment and commercialization of AlN Lamb mode resonators. This dissertation presents comprehensive investigations and solutions to these issues. This thesis is organized as follows: Chapter 1 gives a brief introduction of the basics on piezoelectric MEMS resonators and their promising applications. Chapter 2 first investigates the various available Lamb wave modes in AlN and then identifies the S0 mode as the promising resonator solution to overcome several challenges associated with SOA. Chapter 2 also discusses several outstanding challenges with S0 devices, including spurious mode suppression, Q enhancement, scaling resonant frequency, and enlarging fractional bandwidth. In response, Chapters 3-7 address these outstanding challenges by developing new designs and models, resorting to new acoustic mode, and incorporating new piezoelectric material. More specifically, Chapter 3 proposes two techniques to suppress the spurious modes in the responses of S0 resonators, namely mode conversion and mode shifting. Chapter 4 address the challenge of a conventionally vague question of reflection at the interface between released and unreleased regions in S0 resonators, and then demonstrates Q enhanced resonators with defined released regions achieved by a sandbox process. Chapter 5 first characterizes the S1 Lamb mode and optimizes its resonator configuration. A high-frequency S1 resonator at 3.5 GHz with a coupling of 3.5% is fabricated and demonstrated. Chapter 6 presents a hybrid filtering topology with a mode conversion AlN S0 resonator and lumped elements for widening the bandwidths of resonator-based filters. Chapter 7 proposes lithium niobate (LiNbO3) multilayered resonators with large electromechanical coupling, structure robustness, and good temperature stability. The analysis of Bragg reflectors, resonator simulation, stress control, fabrication, and measurements are covered in this chapter.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Gao, Anming

Contributors dc:contributor

• Gong, Songbin
• Schutt-Ainé, José E.
• Li, Xiuling
• Zhou, Jin

• AlN, RF MEMS, piezoelectric, resonator

Statement dc:rights

• Copyright 2018 Anming Gao

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/102949

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/102949