Numerical Investigation of Phononic Crystal Based Film Bulk Acoustic Wave Resonators.

Linhao Shi,Hao Jin,Shurong Dong,Jikui Luo,Weipeng Xuan,Biao Zhang

doi:10.3390/nano11102547

Abstract

Film bulk acoustic resonator (FBAR)-based filters have attracted great attention because they can be used to build high-performance RF filters with low cost and small device size. Generally, FBARs employ the air cavity and Bragg mirror to confine the acoustic energy within the piezoelectric layer, so as to achieve high quality factors and low insertion loss. Here, two-dimensional (2D) phononic crystals (PhCs) are proposed to be the acoustic energy reflection layer for an FBAR (PhC-FBAR). Four kinds of PhC structures are investigated, and their bandgap diagrams and acoustic wave reflection coefficients are analyzed using the finite element method (FEM). Then, the PhCs are used as the acoustic wave reflectors at the bottom of the piezoelectric stack, with high reflectivity for elastic waves in the specific frequency range. The results show that the specific PhC possesses a wide bandgap, which enables the PhC-FBAR to work at a broad frequency range. Furthermore, the impedance spectra of PhC-FBARs are very smooth with few spurious modes, and the quality factors are close to those of traditional FBARs with air cavities, showing the application potential of the PhC-FBAR filters with wide bandwidth and high power capability.

Highlights

With the continuous advancement of informatization and the rapid development of mobile technology—from smart homes to autonomous vehicles—there is an ever-growing demand for advanced radio frequency (RF) communication systems [1,2]
For the solidly mounted resonator (SMR), the Q decreases drastically when the working frequency is away from the central point, and the reduction in the Q values ranges from 32.2% to 46.5%, while the Q of the phononic crystals (PhCs)-film bulk acoustic resonator (FBAR) remains almost unchanged in the whole width of the frequency range investigated
This work introduces the basic theory of PhC and the calculation method of the band diagram of PhC

Summary

Introduction

With the continuous advancement of informatization and the rapid development of mobile technology—from smart homes to autonomous vehicles—there is an ever-growing demand for advanced radio frequency (RF) communication systems [1,2]. Traditional radio frequency filters are not able to meet the requirements for future wireless communication systems, due to structural and performance inadequacies. The ceramic filters have high power capacity and low insertion loss, but their dimensions are too large to meet the requirements of miniaturization [3]. The size of surface acoustic wave (SAW) filters is small, in the range of hundreds of microns, but they have low power capacity, and their working frequency is relatively low for the forthcoming information era [4,5]. Compared with ceramic and SAW filters, the thin-film bulk acoustic resonator (FBAR) is a kind of high-frequency resonator that has the advantages of small size, low insertion loss, high Q-value, high out-of-band rejection, and high power capacity [6,7,8]; it has received particular attention in recent years

Methods

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Discussion

Conclusion