Acoustic Wave Electrode Structure for Unnecessary Wave Separation
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Solution Overview
Problem
Acoustic wave devices with protective films generate unnecessary waves near anti-resonant frequencies, which can deteriorate filter characteristics.
Innovation Solution
The design includes a piezoelectric substrate with a lithium tantalate or lithium niobate layer, functional electrodes, and a dielectric film where the dielectric film ridge portion has a larger curvature radius than the electrode finger ridge portion, effectively keeping the unnecessary wave frequency away from the anti-resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective film is provided on the piezoelectric layer to cover the electrode, then the electrode is protected, but an unnecessary wave is generated near the anti-resonant frequency which deteriorates filter characteristics
Solution Approach 1:
The patent removes the protective film from the electrode structure. By extracting this problematic component, the source of unnecessary wave generation is eliminated while the electrode remains functional without the protective layer that was causing the interference near anti-resonant frequencies
Solution Approach 2:
Instead of adding a protective film to protect the electrode (conventional approach), the patent inverts the approach by removing the protective film entirely. This reversal eliminates the harmful effect of the protective film while maintaining electrode functionality through alternative design considerations
2Object-generated harmful factors
If the curvature radius of the dielectric film ridge portion is made larger than that of the electrode finger ridge portion, then the unnecessary wave frequency is kept away from anti-resonant frequency, but the manufacturing precision requirement increases
Solution Approach 1:
The patent applies different curvature radius values to different portions of the structure. Specifically, the dielectric film ridge portion is given a larger curvature radius than the electrode finger ridge portion. This local differentiation creates the necessary frequency separation while allowing each portion to be optimized independently for its specific function
Solution Approach 2:
The patent changes the geometric parameter (curvature radius) of the dielectric film ridge portion to be larger than that of the electrode finger ridge portion. This parameter modification shifts the unnecessary wave frequency away from the anti-resonant frequency, resolving the interference issue through controlled dimensional variation
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 maintains the frequency of unnecessary waves at a distance from anti-resonant frequencies, reducing their impact on filter characteristics and improving the performance of acoustic wave devices.
Implementation Method 1
a piezoelectric layer that is provided on the support and includes lithium tantalate or lithium niobate... By applying an alternating-current (AC) voltage between the electrodes, the bulk wave in the thickness shear mode is excited
Implementation Method 2
an acoustic reflection portion overlaps at least a portion of the functional electrode in plan view... both the dielectric film ridge portion and the electrode finger ridge portion have a curved shape, in which a curvature radius of at least a portion of the dielectric film ridge portion is larger than a curvature radius of at least a portion of the electrode finger ridge portion
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate including a support that includes a support substrate, and a piezoelectric layer on the support, a functional electrode on the piezoelectric layer and including a pair of electrode fingers, and a dielectric film covering the pair of electrode fingers. An acoustic reflection portion overlaps at least a portion of the functional electrode in plan view seen along a laminating direction of the support and the piezoelectric layer. Assuming a thickness of the piezoelectric layer is d and a center-to-center distance between adjacent electrode fingers is p, d/p is about 0.5 or less. A dielectric film ridge portion and an electrode finger ridge portion have a curved shape, in which a curvature radius of at least a portion of the dielectric film ridge portion is larger than a curvature radius of at least a portion of the electrode finger ridge portion.