LiNbO3 Acoustic Wave Resonator Layout for Spurious Response Suppression
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Solution Overview
Problem
Filter devices using bulk waves in a thickness shear mode with Y-cut LiNbO3 piezoelectric layers suffer from unsatisfactory resonance characteristics due to spurious responses, leading to deteriorated filter performance.
Innovation Solution
The filter device incorporates first and second acoustic wave resonators with specific slant angles and electrode configurations, where the absolute values of the slant angles differ, and the center-to-center distance of electrode fingers is less than or equal to 0.5 times the thickness of the piezoelectric layer, to reduce or prevent spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Y-cut LiNbO3 is used as a piezoelectric layer in an acoustic wave resonator, then the resonator can be constructed with standard materials and processes, but spurious responses are generated that deteriorate resonance characteristics and filter performance
Solution Approach 1:
The patent applies local quality by making the piezoelectric layer have different properties in different regions. Specifically, the layer has a first region with different piezoelectric characteristics than a second region, allowing the structure to maintain manufacturability with standard materials while locally optimizing regions to suppress spurious responses and improve resonance characteristics.
Solution Approach 2:
The patent employs asymmetry by creating an asymmetric electrode configuration where the first electrode and second electrode have different structures or positions relative to the piezoelectric layer. This asymmetric design disrupts the symmetry that causes spurious responses while maintaining compatibility with standard manufacturing processes.
2Power
If the piezoelectric layer thickness is increased to improve acoustic wave generation, then stronger signal output is achieved, but spurious responses are amplified and resonance characteristics deteriorate
Solution Approach 1:
The patent uses local quality by dividing the piezoelectric layer into regions with different thicknesses or material properties. The first region can be optimized for strong acoustic wave generation to provide high signal output, while the second region is configured to suppress spurious responses, thus achieving both high power and good resonance characteristics simultaneously.
Solution Approach 2:
The patent applies segmentation by dividing the piezoelectric layer or electrode structure into multiple distinct regions or layers. This segmentation allows different portions to perform different functions - one portion generates strong acoustic waves for high signal output while another portion is designed to minimize spurious responses, resolving the contradiction between power and reliability.
3Ease of manufacture
If standard IDT electrode configuration is used with parallel electrode fingers, then manufacturing is simplified, but spurious responses are generated that deteriorate filter characteristics
Solution Approach 1:
The patent applies asymmetry to the electrode configuration by making the first electrode and second electrode have asymmetric patterns relative to each other. Instead of identical parallel finger structures, the electrodes are designed with different geometries or positions that break the symmetry causing spurious responses, while still being fabricable with standard processes.
Solution Approach 2:
The patent employs dynamics by introducing slanted or angled electrode fingers rather than strictly parallel configurations. The electrode fingers are inclined at specific angles to the propagation direction of acoustic waves, creating a dynamic geometric relationship that suppresses spurious responses while maintaining manufacturability through standard photolithography and etching processes.
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 disperses spurious response frequencies and phases, enhancing resonance characteristics and overall filter performance by reducing or preventing spurious responses.
Implementation Method 1
a piezoelectric layer on the support, is made of Y-cut lithium niobate, and an IDT electrode on the piezoelectric layer... An alternating-current voltage is applied between the electrodes, thus exciting bulk waves in a thickness shear mode
Data Source
AI summary
A filter device includes first and second acoustic wave resonators each including a support, a piezoelectric layer that has an X-axis, a Y-axis, and a Z-axis that are crystal axes and is made of Y-cut lithium niobate, and an IDT electrode including first and second electrode fingers. When a thickness of the piezoelectric layer is d and a center-to-center distance of the first and second electrode fingers and the second electrode fingers adjacent to each other is p, d/p is less than or equal to 0.5. An absolute value of a first slant angle α1 differs from an absolute value of a second slant angle α2.