Acoustic Wave Filter Structure for Suppressing SH Spurious Modes
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Solution Overview
Problem
Existing acoustic wave filters in RF communication systems suffer from shear horizontal mode (SH mode) spurious signals that degrade filter performance, particularly in ladder structures, leading to undesirable discontinuities in impedance parameters and reduced efficiency.
Innovation Solution
Incorporating a high velocity layer within the dielectric layer of the acoustic wave device, formed from materials like silicon nitride or aluminum oxide, which enhances acoustic velocity and shifts the frequency of shear wave spurious modes out of the passband, thereby improving filter performance by reducing SH mode intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional acoustic wave filter is used, then the filter structure is simple, but shear horizontal mode spurious signals degrade filter performance
Solution Approach 1:
The dielectric layer is segmented into multiple layers with different acoustic velocities. The first dielectric layer has a first acoustic velocity and the second dielectric layer has a second acoustic velocity different from the first. This segmentation allows different portions of the dielectric layer to serve different functions in suppressing shear horizontal mode spurious signals while maintaining overall filter performance.
Solution Approach 2:
The patent uses composite dielectric structures with layers of different materials or compositions. The first dielectric layer and second dielectric layer have different acoustic velocities, creating a composite structure that suppresses SH mode spurious signals. This composite approach improves reliability by eliminating discontinuities in impedance parameters while managing the increased structural complexity through systematic material selection.
2Reliability
If the dielectric layer is made uniform, then manufacturing is easier, but discontinuities in impedance parameters occur due to shear wave spurious modes
Solution Approach 1:
The uniform dielectric layer is divided into segmented layers with different acoustic velocities. The first dielectric layer and second dielectric layer are fabricated with distinct properties to suppress shear wave spurious modes. This segmentation ensures continuity in impedance parameters across the frequency range while providing clear fabrication guidelines for each layer, balancing manufacturing ease with performance requirements.
Solution Approach 2:
Different regions of the dielectric layer are assigned different acoustic velocities to address local requirements. The first dielectric layer and second dielectric layer have locally optimized properties that suppress SH mode spurious signals in specific frequency ranges. This local quality approach ensures impedance parameter continuity where needed while simplifying fabrication by allowing each layer to be optimized independently.
3Reliability
If a high velocity layer is added to suppress shear horizontal mode, then filter performance improves, but device complexity increases
Solution Approach 1:
The dielectric layer is segmented into functional sections with different acoustic velocities. The first dielectric layer and second dielectric layer are arranged to suppress shear horizontal mode spurious signals at different frequency ranges. This segmentation improves filter performance by eliminating discontinuities while keeping the structural complexity manageable through a systematic two-layer approach rather than adding multiple complex components.
Solution Approach 2:
The patent employs composite dielectric layers with different acoustic velocities to suppress SH mode spurious signals. The first dielectric layer and second dielectric layer form a composite structure that improves filter performance by eliminating impedance discontinuities. This composite material approach enhances reliability while controlling device complexity through purposeful material selection and layer configuration.
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 introduction of a high velocity layer effectively suppresses shear horizontal mode spurious signals, enhancing the frequency response and reducing discontinuities, thus improving the overall performance and efficiency of acoustic wave filters.
Implementation Method 1
the high velocity layer being configured to provide a higher acoustic velocity than the dielectric layer
Data Source
AI summary
Aspects and embodiments disclosed herein include an acoustic wave device comprising a substrate, an interdigital transducer (IDT) electrode disposed on the substrate and configured to generate an acoustic wave in response to an electrical signal, the IDT electrode including a lower layer and an upper layer, a dielectric layer having a height and formed to cover at least a part of the substrate and the IDT electrode, and a high velocity layer embedded within the dielectric layer, the high velocity layer arranged above the IDT electrode and in parallel to an upper surface of the substrate, the high velocity layer being configured to provide a higher acoustic velocity than the dielectric layer.