Laminated Acoustic Wave Resonator Cut Angle for Lower-Side Rayleigh Spurs
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Solution Overview
Problem
Existing acoustic wave devices with a laminate structure suffer from spurious emission of Rayleigh waves on the lower frequency side, leading to deteriorated attenuation characteristics, especially when used in filters connected to antennas.
Innovation Solution
The acoustic wave device incorporates a series of series arm and parallel arm resonators with specific configurations, including piezoelectric layers, high-acoustic-velocity members, and low-acoustic-velocity films, where the thickness of the piezoelectric layer is optimized to reduce spurious emission by adjusting the cut angle of the piezoelectric layer based on specific structural parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a laminate structure including high-acoustic-velocity film, low-acoustic-velocity film, and piezoelectric film is used, then Q value is increased and loss is reduced, but spurious emission of Rayleigh wave is generated on lower frequency side and attenuation characteristics are deteriorated
Solution Approach 1:
The patent changes the cut angle parameter of the piezoelectric layer to suppress Rayleigh wave spurious emission. Specifically, the cut angle is set within a range of θB±4° where θB is calculated based on wavelength, IDT electrode thickness, specific gravity, duty ratio, piezoelectric layer thickness, and low-acoustic-velocity film thickness. This parameter optimization resolves the contradiction by maintaining the beneficial Q value while eliminating the harmful spurious emission.
Solution Approach 2:
The patent uses a composite laminate structure consisting of high-acoustic-velocity film, low-acoustic-velocity film, and piezoelectric film. This composite structure maintains the advantages of reduced acoustic wave loss and increased Q value while the specific cut angle of the piezoelectric layer composite suppresses the generation of Rayleigh wave spurious emission.
2Adaptability or versatility
If existing acoustic wave resonators are configured in a plurality for filter application, then filter functionality is achieved, but spurious emission is generated in the pass band of low frequency-side filter connected to antenna
Solution Approach 1:
The patent applies parameter change to the cut angle of the piezoelectric layer in acoustic wave resonators used for filter applications. By setting the cut angle within θB±4°, the spurious emission is suppressed in the pass band of low frequency-side filters connected to antennas, while maintaining the desired filter functionality and adaptability.
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 configuration effectively reduces spurious emission of Rayleigh waves on the lower frequency side while maintaining or improving the pass band characteristics, thereby enhancing the performance of acoustic wave devices, multiplexers, and communication apparatuses.
Implementation Method 1
Each of the first acoustic wave resonator 3A and the second acoustic wave resonator 3B includes a piezoelectric layer 6A, 6B, an IDT electrode 7A, 7B
Implementation Method 2
In the high-acoustic-velocity member, an acoustic velocity of a bulk wave propagating in the high-acoustic velocity member is higher than an acoustic velocity of an acoustic wave propagating in the piezoelectric layer
Data Source
AI summary
In an acoustic wave device, an antenna end resonator electrically closest to a first terminal is a first acoustic wave resonator. In each of the first acoustic wave resonator and a second acoustic wave resonator, a thickness of a piezoelectric layer is equal to or less than about 3.5λ. A cut angle of the piezoelectric layer of the first acoustic wave resonator is within a range of θB±4°. The cut angle of the piezoelectric layer of the second acoustic wave resonator has a larger difference from θB (°) than the cut angle of the piezoelectric layer of the first acoustic wave resonator.