XBAR Diaphragm Resonator Geometry for Spurious Mode Suppression
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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 limitations in design trade-offs such as insertion loss, rejection, isolation, power handling, linearity, size, and cost, and are plagued by spurious modes that degrade filter performance.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with a thin film conductor pattern on a piezoelectric plate, utilizing a diaphragm structure and interdigital transducers to excite primary shear acoustic modes, which offer high piezoelectric coupling and are suitable for frequencies above 3 GHz, while minimizing spurious modes through optimized IDT pitch and mark-to-pitch ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used for RF filters, then the filters can operate at lower frequencies, but they cannot achieve satisfactory performance for higher frequency communications bands above 3 GHz due to design trade-offs and spurious modes
Solution Approach 1:
The patent changes the excitation mode parameter from longitudinal to transverse shear modes, and optimizes geometric parameters including IDT pitch and mark-to-pitch ratios. This parameter transformation enables the resonator to operate effectively at higher frequencies above 3 GHz while maintaining reliable filter performance and eliminating spurious modes that plague conventional designs
2Reliability
If the IDT pitch and mark-to-pitch ratios are optimized to reduce spurious modes, then filter performance is improved, but the device design becomes more complex
Solution Approach 1:
The patent establishes specific parameter ranges for IDT pitch (0.5-2.0 times the thickness of the piezoelectric film) and mark-to-pitch ratios (0.2-0.4) that systematically reduce spurious modes. By defining these parameter relationships, the patent transforms a complex design problem into a standardized configuration that achieves spurious mode reduction without excessive design complexity
3Reliability
If transversely-excited film bulk acoustic resonators with optimized parameters are used, then spurious modes are reduced and piezoelectric coupling is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent defines specific parameter ranges for IDT pitch (0.5-2.0 times film thickness) and mark-to-pitch ratios (0.2-0.4) that provide manufacturing tolerance. These parameter specifications enable manufacturers to achieve the desired spurious mode suppression and piezoelectric coupling enhancement while maintaining practical manufacturing precision requirements
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 for RF filters by achieving higher piezoelectric coupling (>20%) and reducing spurious modes, enabling the design of microwave and millimeter-wave filters with wider bandwidths and reduced insertion loss, thus addressing the limitations of existing technologies for future communication systems.
Implementation Method 1
utilizing a diaphragm structure and interdigital transducers to excite primary shear acoustic modes
Implementation Method 2
transversely-excited film bulk acoustic resonators (XBARs) with a thin film conductor pattern on a piezoelectric plate
Implementation Method 3
excite primary shear acoustic modes, which offer high piezoelectric coupling and are suitable for frequencies above 3 GHz
Data Source
AI summary
Acoustic filters, resonators and methods are disclosed. An acoustic resonator includes a substrate and a piezoelectric plate including a diaphragm that spans a cavity in the substrate. A conductor pattern includes an interdigital transducer (IDT) with interleaved parallel fingers on the diaphragm. A ratio of a width of either of two adjacent parallel fingers and a center-to-center spacing between the two adjacent parallel fingers is greater than or equal to 0.2 and less than or equal to 0.3.