LiNbO3 Acoustic Wave Electrode Layout for Resonance Control
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Solution Overview
Problem
Acoustic wave devices using bulk waves in a thickness shear mode with Z-cut LiNbO3 as a piezoelectric layer often fail to achieve satisfactory resonance characteristics.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer made of Z-cut lithium niobate with specific geometric configurations, including IDT electrodes with busbars and electrode fingers, where the thickness of the piezoelectric layer (d) to the center-to-center distance of electrode fingers (p) ratio (d/p) is less than or equal to about 0.5, and the slant angle (α) between the envelope of electrode fingers and the Y-axis direction satisfies certain conditions (e.g., about 9°≤|α|≤about 14° or |α|<about 9° or about 14°<|α|≠0°), enhancing resonance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Z-cut LiNbO3 is used as a piezoelectric layer in an acoustic wave device, then the device can operate with bulk waves in a thickness shear mode, but satisfactory resonance characteristics cannot be obtained
Solution Approach 1:
The patent changes the crystal orientation parameter from standard Z-cut to a specific rotation angle range (10-30 degrees from the Z-axis toward the X-axis). This parameter modification enables the piezoelectric layer to simultaneously support thickness shear mode operation and achieve satisfactory resonance characteristics, resolving the contradiction between material suitability and performance quality.
2Reliability
If the piezoelectric layer thickness d is increased to improve resonance characteristics, then the d/p ratio increases, but this may adversely affect device performance
Solution Approach 1:
The patent establishes a specific parameter range for the thickness-to-pitch ratio (0.2 < d/p ≤ 0.5) that optimizes resonance characteristics while controlling the piezoelectric layer thickness. This parameter optimization resolves the contradiction by identifying the optimal thickness range that achieves good resonance performance without excessive thickness increase.
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 achieves steep impedance-frequency characteristics, reduces insertion loss, and effectively disperses spurious responses, thereby improving the overall filter characteristics of the device.
Implementation Method 1
a piezoelectric layer on the support, the piezoelectric layer including an X-axis, a Y-axis, and a Z-axis that are crystal axes and being made of Z-cut lithium niobate, and an IDT electrode on the piezoelectric layer... An alternating-current voltage is applied between the electrodes, thereby exiting bulk waves in a thickness shear mode
Data Source
AI summary
An acoustic wave device includes a support, a piezoelectric layer on the support, 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 adjacent to each other is p, d/p is less than or equal to about 0.5. When an imaginary line connecting tips of the first electrode fingers is an envelope, a direction in which the envelope extends and the direction of the Y-axis intersect each other, and about 9°≤|α|≤about 14° is satisfied, where |α| is an absolute value of a slant angle α. The slant angle α is an angle of a corner defined by the direction in which the envelope extends and the direction of the Y-axis and is an angle other than 0°.