XBAR IDT Mark and Pitch Layout for Cleaner RF Resonance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands, such as those proposed for future wireless networks, due to limitations in design trade-offs between performance parameters like insertion loss, rejection, isolation, power handling, linearity, size, and cost, particularly at frequencies above 3 GHz.
Innovation Solution
The development of transversely-excited film bulk acoustic resonators (XBARs) with interdigital transducers (IDTs) featuring varied pitch and mark configurations along the length or across the aperture, which effectively reduce spurious modes and enhance frequency selectivity, allowing for improved performance at higher frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic wave resonators are used for higher frequency bands, then existing design trade-offs are maintained, but performance parameters such as insertion loss, rejection, and frequency selectivity deteriorate at frequencies above 3 GHz
Solution Approach 1:
The IDT fingers are configured with non-uniform pitch and/or mark variations across different regions of the transducer. This local variation in geometric parameters creates different acoustic coupling characteristics in different zones, enabling suppression of spurious modes while maintaining strong fundamental mode coupling, thereby improving frequency selectivity for higher frequency bands
Solution Approach 2:
The patent changes the geometric parameters (pitch and mark) of the IDT fingers to optimize acoustic wave generation. By varying these parameters across the transducer aperture, the design achieves better control over acoustic mode excitation, improving performance at higher frequencies while maintaining adaptability
2Ease of manufacture
If uniform pitch and mark are used in the IDT, then manufacturing is simplified, but spurious modes are not sufficiently reduced
Solution Approach 1:
The IDT incorporates regions with different pitch and mark values to create localized variations in acoustic coupling. These local quality differences are designed to suppress spurious modes that would otherwise be generated by uniform structures, while still allowing for practical manufacturing using standard lithographic processes
Solution Approach 2:
The patent introduces asymmetric variations in the IDT finger geometry, where pitch and mark values differ across the transducer aperture. This asymmetry disrupts the generation of symmetric spurious modes while maintaining the desired fundamental mode, effectively reducing harmful acoustic modes without requiring complex manufacturing
3Power
If the IDT aperture is increased to improve power handling, then power handling capability is enhanced, but spurious modes increase
Solution Approach 1:
The IDT is designed with non-uniform pitch and mark distributions across its aperture. This allows different regions of the transducer to contribute differently to acoustic wave generation, enabling the aperture to be sufficiently large for high power handling while certain regions suppress spurious mode generation through optimized local geometric parameters
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 XBARs with varied pitch and mark configurations demonstrate reduced spurious modes and improved frequency selectivity, enabling better performance in RF filters for higher frequency bands, thereby enhancing communication system capabilities such as larger cell size, longer battery life, higher data rates, and greater network capacity.
Implementation Method 1
an interdigital transducer (IDT) comprising a first plurality of fingers extending from a first busbar and a second plurality of fingers extending from a second busbar
Implementation Method 2
acoustic wave resonators including surface acoustic wave (SAW) resonators, bulk acoustic wave BAW) resonators, film bulk acoustic wave resonators (FBAR)
Data Source
AI summary
Acoustic resonator devices and filters are disclosed. An acoustic resonator includes a piezoelectric plate having front and back surfaces and an interdigital transducer (IDT). The IDT has a first pitch/mark zone with interleaved fingers having a pitch equal to a first pitch value P1 and a mark equal to a first mark value M1, and a second pitch/mark zone with interleaved fingers having a pitch equal to a second pitch value P2 and a mark equal to a second mark value M2. A radio frequency signal applied to the IDT causes excitation of a same shear primary acoustic mode by both the first pitch/mark zone and the second pitch/mark zone. P1, M1, P2, and M2, are selected such that an amplitude of spurious modes is reduced as compared to a device having a same primary acoustic mode and a single pitch/mark zone.