XBAR Oxide Strip Aperture Margins for Oblique Wave Suppression
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as the 5G NR standard, which necessitates the development of more effective bandpass filters capable of handling higher transmit power and wider communication channel bandwidths.
Innovation Solution
The implementation of a Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with an oxide strip acoustic confinement structure, which enhances the Bode Q factor and improves the performance of RF filters by suppressing unwanted oblique waves and increasing the efficiency of acoustic energy propagation, thereby enabling better performance at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used, then device structure is simple, but performance at higher frequencies and wider bandwidths is insufficient
Solution Approach 1:
The resonator structure is segmented into distinct functional layers: piezoelectric layer, acoustic confinement layer with oxide strips, and substrate. This segmentation allows each layer to be optimized independently for high-frequency performance while maintaining manufacturability.
Solution Approach 2:
The resonator employs composite material structure combining piezoelectric material with acoustic confinement materials (oxide strips), creating a composite resonator that achieves both high-frequency operation and acoustic energy confinement, resolving the contradiction between performance and complexity.
2Reliability
If acoustic confinement structures are added to suppress oblique waves, then Bode Q factor is improved, but device complexity increases
Solution Approach 1:
Acoustic confinement is applied locally at critical regions where oblique waves are generated (at the edges of the interdigital transducer), rather than throughout the entire resonator. The oxide strips are positioned specifically at the aperture edges to suppress oblique wave generation at these critical locations, improving Bode Q factor while minimizing added complexity.
Solution Approach 2:
The oxide strips act as intermediary acoustic confinement structures that mediate between the interdigital transducer and the acoustic wave propagation path, suppressing oblique waves without requiring complex active control or additional transducer elements.
3Loss of energy
If oxide strip acoustic confinement structures are implemented, then unwanted oblique waves are suppressed and acoustic energy propagation efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The acoustic confinement is achieved by controlling material parameters (oxide strip thickness, width, and position) rather than requiring complex geometric structures. By optimizing these parameters, the oxide strips effectively suppress oblique waves and reduce acoustic energy loss while maintaining compatibility with standard thin-film fabrication processes.
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
The XBAR with oxide strip acoustic confinement structures achieves improved Bode Q factors and filter performance, particularly at the lower band edge, allowing for effective operation in higher frequency bands like n77 and n79, and millimeter wave communication bands, enhancing the sharpness of filter transfer functions and reducing losses.
Implementation Method 1
oxide strip acoustic confinement structures which enhance the Bode Q factor and improves the performance of RF filters by suppressing unwanted oblique waves and increasing the efficiency of acoustic energy propagation
Implementation Method 2
Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with an oxide strip acoustic confinement structure, which enhances the Bode Q factor and improves the performance of RF filters
Data Source
AI summary
Acoustic resonators, filters, and methods. An acoustic resonator includes a substrate, piezoelectric plate, and a diaphragm comprising a portion of the piezoelectric plate spanning a cavity in a substrate. An interdigital transducer (IDT) on a front surface of the piezoelectric plate includes first and second sets of interleaved interdigital transducer (IDT) fingers extending from first and second busbars respectively. The interleaved IDT fingers are on the diaphragm. Overlapping portions of the interleaved IDT fingers define an aperture of the acoustic resonator. A first dielectric strip overlaps the IDT fingers in a first margin of the aperture and extends into a first gap between the first margin and the first busbar. A second dielectric strip overlaps the IDT fingers in a second margin of the aperture and extends into a second gap between the second margin and the second busbar.