SAW Filter Acoustic Velocity Structure 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 to create different acoustic velocity regions, reducing radiation losses and maintaining uniform IDT electrode pitches, thereby simplifying manufacturing and improving frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If varying interdigital transducer electrode pitches are used to achieve desired frequency responses, then frequency response can be adjusted, but radiation losses increase and manufacturing difficulty increases
Solution Approach 1:
The patent introduces an acoustic velocity adjustment structure with spatially varying properties (different layers in different regions) to achieve frequency response control without varying the IDT electrode pitch. This allows uniform electrodes to maintain low radiation losses while the localized velocity adjustments provide the needed frequency selectivity.
Solution Approach 2:
The acoustic velocity adjustment structure acts as an intermediary between the uniform IDT electrodes and the desired frequency response. Instead of directly varying electrode pitch, the patent uses this intermediate structure with controlled acoustic velocity variations to achieve frequency selectivity while maintaining electrode uniformity.
2Manufacturing precision
If varying interdigital transducer electrode pitches are used to achieve desired frequency responses, then frequency response can be adjusted, but manufacturing difficulty increases
Solution Approach 1:
The patent introduces an acoustic velocity adjustment structure with spatially varying properties (different layers in different regions) to achieve frequency response control without varying the IDT electrode pitch. This allows uniform electrodes to maintain low radiation losses while the localized velocity adjustments provide the needed frequency selectivity.
Solution Approach 2:
The acoustic velocity adjustment structure acts as an intermediary between the uniform IDT electrodes and the desired frequency response. Instead of directly varying electrode pitch, the patent uses this intermediate structure with controlled acoustic velocity variations to achieve frequency selectivity while maintaining electrode uniformity.
3Reliability
If acoustic velocity adjustment structure is added to reduce radiation losses, then quality factor improves, but device complexity increases
Solution Approach 1:
Instead of varying properties in the horizontal plane (electrode pitch), the patent introduces vertical layering with different acoustic velocity layers. This dimensional transition from 2D electrode variation to 3D velocity profiling allows quality factor improvement through controlled velocity variations without complicating the electrode structure.
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 acoustic velocity adjustment structure reduces radiation losses and allows for higher frequency filtering with reduced bulk radiation, achieving a high quality factor and uniform pitch variations, thus enhancing the performance of multimode SAW filters.
Implementation Method 1
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 2
The high speed layer can include a silicon nitride layer. The high speed layer can include an aluminum oxide layer.
Implementation Method 3
The low speed layer can be configured to decrease the acoustic wave propagation velocity in the third region relative to the second region
Implementation Method 4
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
Data Source
AI summary
Aspects of this disclosure relate to a surface acoustic wave filter with an acoustic velocity adjustment structure. The surface acoustic wave filter can include a first interdigital transducer electrode disposed on a piezoelectric layer, an acoustic reflector disposed on the piezoelectric layer, and a second interdigital transducer electrode disposed on the piezoelectric layer. The second interdigital transducer electrode is longitudinally coupled to the first interdigital transducer electrode and positioned between the first interdigital transducer electrode and the acoustic reflector. The acoustic velocity adjustment structure can be positioned over at least a gap between the first interdigital transducer electrode and the second interdigital transducer electrode. The acoustic velocity adjustment structure can be 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.