XBAR RF Filter Layout Using Shared Acoustic Tracks for Wide Bandwidth
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Solution Overview
Problem
Existing RF filters using acoustic wave resonators are not well-suited for the higher frequencies and wider bandwidths required by future communications networks, such as the 5G NR standard, particularly in bands n77, n79, and WiFi bands at 5 GHz and 6 GHz, due to limitations in design and manufacturing methods.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with shared acoustic tracks in RF filters, which allows for smaller footprint, reduced manufacturing costs, and improved performance by acoustically coupling resonators on a single diaphragm, enabling efficient operation in high-frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used in RF filters, then the filters can operate at traditional frequencies, but they cannot achieve the higher frequencies and wider bandwidths required by future communications networks
Solution Approach 1:
The patent changes the fundamental operating parameters of the acoustic resonators by transitioning from surface acoustic wave (SAW) modes to bulk acoustic wave (BAW) modes, specifically using transverse bulk acoustic waves. This parameter change enables operation at higher frequencies (above 3 GHz) and wider bandwidths required for 5G NR bands n77 and n79, while maintaining the necessary filter performance characteristics
Solution Approach 2:
The patent replaces the conventional SAW resonator mechanical system with a BAW resonator system that uses transverse bulk acoustic waves propagating through a piezoelectric film. This substitution of the acoustic wave mechanism enables higher frequency operation and improved performance for future communication networks
2Ease of manufacture
If multiple separate acoustic resonators are used in RF filters, then each resonator can be independently designed, but the filter footprint becomes larger and manufacturing costs increase
Solution Approach 1:
The patent merges multiple acoustic resonators into a single integrated structure where multiple resonators share common acoustic tracks and propagate acoustic waves through a shared piezoelectric film substrate. This merging reduces the overall filter footprint and simplifies manufacturing by reducing the number of separate components that need to be assembled
Solution Approach 2:
The shared piezoelectric film substrate serves multiple functions simultaneously: it acts as the acoustic waveguide for multiple resonators, provides mechanical support for all resonators, and enables acoustic coupling between resonators. This multi-functionality reduces the overall device complexity and manufacturing cost
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
XBARs with shared acoustic tracks provide high electromechanical coupling and frequency capability, reducing filter size and manufacturing costs while enhancing performance in high-frequency applications, supporting wider bandwidths and higher power handling.
Implementation Method 1
The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Data Source
AI summary
Acoustic filters devices and methods of making the same. A filter device includes a plurality of series resonators acoustically coupled along a first shared acoustic track and a plurality of shunt resonators acoustically coupled along a second shared acoustic track and electrically coupled to the plurality of series resonators.