XBAR Buried Oxide Strip Layout for High-Q RF Filtering
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Solution Overview
Problem
Current RF filters, particularly those 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 includes bands like n77, n79, and millimeter wave frequencies, leading to performance limitations in terms of insertion loss, rejection, and bandwidth handling.
Innovation Solution
The development of a Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with buried oxide strip acoustic confinement structures, which enhances the Bode Q factor and improves frequency handling by suppressing unwanted oblique waves and increasing piezoelectric coupling, enabling better performance in high-frequency applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used, then device simplicity is maintained, but frequency handling capability and Bode Q factor are insufficient for higher frequencies and wider bandwidths
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 its specific function, enabling high frequency handling while maintaining manufacturing feasibility
Solution Approach 2:
The acoustic confinement layer with oxide strips acts as an intermediary between the piezoelectric layer and substrate. This intermediate structure confines acoustic energy laterally, improving Bode Q factor and frequency handling capability without requiring complete redesign of the entire resonator system
2Reliability
If acoustic confinement structures are added to enhance Bode Q factor, then frequency handling improves, but manufacturing complexity increases
Solution Approach 1:
The oxide strip width, spacing, and thickness are carefully controlled within specific parameter ranges to achieve optimal acoustic confinement. By optimizing these geometric parameters, high Bode Q factor is achieved using standard semiconductor fabrication techniques, balancing performance with manufacturability
3Productivity
If higher frequencies are supported, then bandwidth handling improves, but insertion loss and rejection performance deteriorate
Solution Approach 1:
The acoustic confinement structures maintain continuous acoustic energy confinement across the operating frequency range. This continuous confinement minimizes energy leakage and maintains low insertion loss even at higher frequencies and wider bandwidths, enabling 5G NR band performance
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 buried oxide strip acoustic confinement structures achieves improved Bode Q factors and frequency handling, effectively addressing the limitations of existing RF filters by enhancing the sharpness of filter transfer functions and reducing losses, thus supporting higher frequency and wider bandwidth requirements.
Implementation Method 1
a thin plate of piezoelectric material bonded to a substrate
Implementation Method 2
buried oxide strip acoustic confinement structures, which enhances the Bode Q factor and improves frequency handling by suppressing unwanted oblique waves
Implementation Method 3
Transversely-Excited Film Bulk Acoustic Resonator (XBAR) with buried oxide strip acoustic confinement structures, which enhances the Bode Q factor and improves frequency handling
Data Source
AI summary
Acoustic resonators, filters, and methods. An acoustic resonator includes a substrate, a piezoelectric plate, and a diaphragm including 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 extend onto the diaphragm. Overlapping portions of the interleaved IDT fingers define an aperture of the acoustic resonator. First and second dielectric strips are on the front surface of the piezoelectric plate. Each dielectric strip has a first portion under the IDT fingers in a respective margin of the aperture and a second portion extending into a gap between the respective margin and the respective busbar.