LiTaO3 SAW Filter Cut Angle Tuning for Spurious Response Suppression
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Solution Overview
Problem
Surface acoustic wave filters using multilayer bodies experience Rayleigh wave spurious responses on the lower frequency side, leading to degraded attenuation characteristics, especially when used in multiplexers, due to the lack of a unique cut angle for the piezoelectric substrate that optimizes filter characteristics.
Innovation Solution
A surface acoustic wave filter with a LiTaO3 piezoelectric layer having a cut angle θ°, a high acoustic velocity support substrate, a low acoustic velocity film, and an IDT electrode, where the cut angle θ is optimized based on structural parameters such as the repetition period, film thickness, specific gravity, and electrode duty to minimize Rayleigh wave spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a multilayer body with high acoustic velocity support substrate, low acoustic velocity film, and piezoelectric layer is used to increase Q-value, then low loss properties are improved, but Rayleigh wave spurious response generates on the lower frequency side causing attenuation characteristics to degrade
Solution Approach 1:
The patent applies parameter changes by optimizing the cut angle of the piezoelectric substrate based on specific structural parameters (wavelength, electrode film thickness, specific gravity, electrode duty, piezoelectric layer thickness, low acoustic velocity film thickness). This mathematical relationship determines the optimal cut angle to minimize Rayleigh wave spurious response while maintaining low loss properties in the pass band.
2Object-generated harmful factors
If the cut angle of the piezoelectric substrate is fixed to suppress spurious response, then attenuation characteristics improve, but filter characteristics cannot be optimized for different structural parameters
Solution Approach 1:
The patent implements dynamics by making the cut angle adjustable and adaptable rather than fixed. The cut angle is determined dynamically based on the specific structural parameters of each filter design, allowing the system to optimize both spurious response suppression and filter characteristics for different applications.
Solution Approach 2:
The patent uses parameter changes by establishing a mathematical relationship between the cut angle and multiple structural parameters (wavelength, electrode film thickness, specific gravity, electrode duty, piezoelectric layer thickness, low acoustic velocity film thickness). This allows the cut angle to be customized for different filter designs while consistently minimizing spurious response.
3Reliability
If structural parameters of IDT electrode and piezoelectric material are optimized for filter characteristics, then pass band performance improves, but Rayleigh wave spurious response increases on the lower frequency side
Solution Approach 1:
The patent resolves this contradiction by introducing the cut angle as an additional optimization parameter. By determining the optimal cut angle based on the structural parameters already required for filter characteristics, the patent simultaneously optimizes both pass band performance and spurious response suppression without requiring separate optimizations.
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 optimized cut angle θ reduces spurious responses in the attenuation band on the lower frequency side, ensuring low loss properties in the pass band and improved filter characteristics, enabling high attenuation and isolation in multiplexers.
Implementation Method 1
a LiTaO3 piezoelectric layer having a cut angle θ°
Implementation Method 2
surface acoustic wave filter
Implementation Method 3
a high acoustic velocity support substrate in which a bulk wave propagates at a higher acoustic velocity than an acoustic wave propagating in the LiTaO3 piezoelectric layer, a low acoustic velocity film which is between the high acoustic velocity support substrate and the LiTaO3 piezoelectric layer, and in which a bulk wave propagates at a lower acoustic velocity than the acoustic wave propagating in the LiTaO3 piezoelectric film
Data Source
AI summary
A filter includes a LiTaO3 piezoelectric layer having a cut angle, a high acoustic velocity support substrate, a low acoustic velocity film, and an IDT electrode. A cut angle θB of the piezoelectric layer at which a Rayleigh wave spurious response is locally reduced or minimized is determined from a wavelength of the IDT electrode, a film thickness of the IDT electrode, a specific gravity of the IDT electrode, an electrode duty, a thickness of the piezoelectric layer, and a film thickness of the low acoustic velocity film. The Cut angle of the piezoelectric layer satisfies a relationship of θB−4≤θ≤θB+4.