Transverse XBAR Resonator Layout for High-Frequency RF Filtering
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Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands above 3 GHz, particularly in future wireless communication systems, due to inefficiencies in design and performance at higher frequencies.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with specific design features such as a thin film conductor pattern on a piezoelectric plate, an interdigital transducer, and a cavity structure, which excite primary shear acoustic modes and reduce spurious modes by optimizing the IDT pitch and mark-to-pitch ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional acoustic wave resonators are used for RF filters, then the filters work for traditional frequency bands, but they are not well-suited for higher frequency communications bands above 3 GHz
Solution Approach 1:
The patent changes the excitation mode parameter from longitudinal to transverse, and optimizes geometric parameters including IDT pitch (λ/4 to λ/6) and mark-to-pitch ratio (0.2 to 0.4), enabling the resonator to operate efficiently at higher frequencies above 3 GHz while maintaining reliability
Solution Approach 2:
The invention transitions from conventional longitudinal excitation to transverse excitation, utilizing shear horizontal acoustic waves that propagate perpendicular to the IDT fingers, thereby enabling high-frequency operation with reduced spurious modes
2Speed
If higher frequency operation is achieved, then bandwidth and performance improve, but spurious modes increase
Solution Approach 1:
By optimizing the IDT pitch to λ/4 to λ/6 and mark-to-pitch ratio to 0.2 to 0.4, the patent suppresses spurious modes while maintaining high-frequency operation, directly addressing the harmful effects that typically increase with frequency
Solution Approach 2:
The patent converts the potential harm of spurious modes into a benefit by using transverse excitation with optimized geometry, where the shear horizontal wave mode naturally suppresses spurious resonances that would otherwise occur at higher frequencies
3Reliability
If transverse excitation with optimized IDT geometry is used, then spurious modes are reduced and piezoelectric coupling is enhanced, but device complexity increases
Solution Approach 1:
The patent establishes specific parameter ranges (pitch: λ/4 to λ/6, mark-to-pitch ratio: 0.2 to 0.4) that achieve high piezoelectric coupling and spurious mode suppression, balancing the trade-off between performance enhancement and manufacturing complexity
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 provide improved performance and bandwidth for high-frequency applications, achieving high piezoelectric coupling and reducing spurious modes, enabling the design of efficient RF filters for frequencies up to 28 GHz.
Implementation Method 1
an interdigital transducer, and a cavity structure, which excite primary shear acoustic modes
Implementation Method 2
transversely-excited film bulk acoustic resonators (XBARs) with specific design features such as a thin film conductor pattern on a piezoelectric plate
Data Source
AI summary
Acoustic filters, resonators and methods are disclosed. An acoustic resonator device includes a piezoelectric plate forming a diaphragm and a conductor pattern formed on the piezoelectric plate, the conductor pattern including an interdigital transducer (IDT). Interleaved fingers of the IDT are on the diaphragm. A ratio of the mark of the interleaved fingers to a pitch of the interleaved fingers is greater than or equal to 0.2 and less than or equal to 0.3.