SAW Filter Velocity Adjustment Layers for Lower Radiation Loss
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Solution Overview
Problem
Multimode surface acoustic wave (SAW) filters face challenges in reducing radiation losses and achieving desired frequency responses due to varying interdigital transducer (IDT) electrode pitches, which can lead to manufacturing difficulties and loss mechanisms that are hard to quantify and model.
Innovation Solution
Incorporating an acoustic velocity adjustment structure with high and low speed layers over specific regions of the SAW device, allowing for controlled acoustic wave propagation velocities without varying the IDT electrode pitch, thereby creating distinct velocity regions and reducing radiation losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the IDT electrode pitch is varied to achieve desired frequency response, then the frequency response is improved, but manufacturing difficulty increases and radiation losses occur
Solution Approach 1:
The patent applies local quality by introducing an acoustic velocity adjustment structure with spatially varying properties. The structure has different acoustic velocities in different regions (first region with higher velocity, second region with lower velocity), allowing localized control of acoustic wave propagation without changing the overall IDT electrode pitch. This enables frequency response optimization while maintaining uniform manufacturing parameters.
Solution Approach 2:
The patent changes the acoustic velocity parameter of the substrate structure rather than changing the geometric pitch of IDT electrodes. By modifying the acoustic velocity parameter through material composition or structural configuration in different regions, the patent achieves frequency response control without varying electrode pitch, thereby simplifying manufacturing.
2Measurement precision
If the IDT electrode pitch is varied to achieve desired frequency response, then the frequency response is improved, but radiation losses increase
Solution Approach 1:
The acoustic velocity adjustment structure creates regions with different acoustic velocities to control wave propagation locally. The first region with higher acoustic velocity and second region with lower acoustic velocity work together to guide acoustic waves through the structure, reducing radiation losses while achieving the desired frequency response without pitch variation.
3Manufacturing precision
If the IDT electrode pitch is kept uniform to simplify manufacturing, then manufacturing precision is improved, but frequency response control becomes difficult
Solution Approach 1:
The patent maintains uniform IDT electrode pitch for manufacturing precision while introducing an acoustic velocity adjustment structure with non-uniform properties. The structure has spatially varying acoustic velocities that provide local control over wave propagation, enabling frequency response optimization without sacrificing manufacturing uniformity.
Solution Approach 2:
Instead of controlling frequency response through one-dimensional pitch variation of IDT electrodes, the patent transitions to controlling it through the acoustic velocity distribution in the substrate structure. This dimensional shift allows frequency response control while maintaining uniform electrode geometry, simplifying manufacturing.
4Speed
If the acoustic velocity is increased in the first region, then the acoustic wave propagation velocity is improved, but the structure complexity increases
Solution Approach 1:
The acoustic velocity adjustment structure implements local quality by having different acoustic velocities in different regions. The first region has higher acoustic velocity to speed up wave propagation where needed, while the second region has lower acoustic velocity. This localized velocity control achieves performance improvement without requiring complex overall structural changes.
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
This approach enables the creation of SAW filters with reduced radiation losses and improved frequency responses, achieving higher quality factors and filtering higher frequency signals with less pitch variation, making them suitable for applications like 5G NR and 4G LTE bands.
Implementation Method 1
A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer
Implementation Method 2
The acoustic velocity adjustment structure is arranged to increase an acoustic wave propagation velocity in a first region that includes the gap relative to a second region over at least a portion of the first interdigital transducer electrode
Implementation Method 3
The acoustic velocity adjustment structure includes a high speed layer over the first region to increase the acoustic wave propagation velocity in the first region. The high speed layer can include a silicon nitride layer. The high speed layer can include an aluminum oxide layer.
Data Source
AI summary
Aspects of this disclosure relate to a surface acoustic wave device that includes a first reflector over a piezoelectric layer, a second reflector over the piezoelectric layer, and an interdigital transducer electrode structure over the piezoelectric layer and positioned between the first reflector and the second reflector. The surface acoustic wave device includes a velocity adjustment layer arranged to adjust acoustic velocity in a region of the surface acoustic wave device. The velocity adjustment layer can be a high speed layer or a low speed layer.