Abstract
With the rapid commercialization of fifth generation (5G) technology in the world, the market demand for radio frequency (RF) filters continues to grow. Acoustic wave technology has been attracting great attention as one of the effective solutions for achieving high-performance RF filter operations while offering low cost and small device size. Compared with surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators have more potential in fabricating high- quality RF filters because of their lower insertion loss and better selectivity in the middle and high frequency bands above 2.5 GHz. Here, we provide a comprehensive review about BAW resonator researches, including materials, structure designs, and characteristics. The basic principles and details of recently proposed BAW resonators are carefully investigated. The materials of poly-crystalline aluminum nitride (AlN), single crystal AlN, doped AlN, and electrode are also analyzed and compared. Common approaches to enhance the performance of BAW resonators, suppression of spurious mode, low temperature sensitivity, and tuning ability are introduced with discussions and suggestions for further improvement. Finally, by looking into the challenges of high frequency, wide bandwidth, miniaturization, and high power level, we provide clues to specific materials, structure designs, and RF integration technologies for BAW resonators.
Highlights
The rapid development of wireless communication applications has led to the urgent requirement for wide bandwidth and high-speed data transmissions
The bulk acoustic wave (BAW) resonator is a piezoelectric stack structure consisting of a piezoelectric film large bandwidth, up to 10%, is a difficult problem for a BAW filter based on aluminum nitride sandwiched between two metallic electrodes
We summarize the existing technologies of Regardless of the electrodes, the resonant frequency depends on the acoustic velocity and the BAW resonators, and discuss merits of various piezoelectric and electrode materials in high-coupling, thickness of the piezoelectric film: large-bandwidth, high-performance designs
Summary
The rapid development of wireless communication applications has led to the urgent requirement for wide bandwidth and high-speed data transmissions. AlN is still the preferential material for bulk production of BAW devices, but the most limiting property is probably the coupling coefficient. AlN is still the preferential material for bulk production of BAW devices, but the most limiting mechanical wave generated by the excitation is twice the thickness of the piezoelectric layers. We summarize the existing technologies of Regardless of the electrodes, the resonant frequency depends on the acoustic velocity and the BAW resonators, and discuss merits of various piezoelectric and electrode materials in high-coupling, thickness of the piezoelectric film: large-bandwidth, high-performance designs. A new design of laterally-excited bulk-wave resonators (XBAR) with ~25% strong piezoelectric coupling and a RF integration technology are proposed for further improving the properties of BAW devices, enhancing the availability of BAW resonators and filters in RF communication
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