Thickness Shear Acoustic Wave Edge Regions for Spurious Control
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Solution Overview
Problem
Existing acoustic wave devices using thickness shear vibration in piezoelectric thin film resonators face challenges in reducing spurious due to standing waves, and the addition of additional structures in the edge region does not sufficiently address this issue, while also making the formation of additional films difficult as resonant frequency increases.
Innovation Solution
The acoustic wave device incorporates a piezoelectric substrate with a pair of electrodes exciting thickness shear vibration, featuring an edge region with distinct acoustic velocity profiles and additional film configurations that differ in width and thickness to achieve a piston mode, reducing spurious by making the acoustic velocity in the edge regions less than the center region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If additional structures are added to the edge region to control acoustic velocity, then spurious reduction is achieved, but device complexity increases and manufacturing difficulty increases at higher resonant frequencies
Solution Approach 1:
The patent applies local quality by creating distinct acoustic velocity regions within the piezoelectric substrate. The edge region is designed with different acoustic velocity characteristics compared to the center region, allowing localized control of acoustic wave propagation. This is achieved through specific crystal orientation and structural design in the edge region, which reduces spurious without requiring additional complex structures throughout the entire device.
Solution Approach 2:
The patent employs asymmetry by making the acoustic velocity in the edge region different from the center region. This velocity difference creates asymmetric acoustic wave propagation characteristics that prevent standing wave formation. The edge region structure is deliberately designed to be asymmetric relative to the center region, enabling effective spurious reduction while maintaining manufacturing feasibility.
2Object-generated harmful factors
If additional structures are added to the edge region to control acoustic velocity, then spurious reduction is achieved, but ease of manufacture deteriorates as resonant frequency increases
Solution Approach 1:
The patent applies parameter changes by modifying the acoustic velocity parameter in the edge region through crystal orientation and structural design. By changing the acoustic velocity parameter locally in the edge region, the patent achieves spurious reduction without requiring additional films or complex structures that would be difficult to manufacture at high resonant frequencies. This parameter-based approach maintains manufacturing simplicity.
3Object-generated harmful factors
If the acoustic velocity in the edge region is made less than the center region, then spurious is reduced, but the structural design complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the piezoelectric substrate into distinct functional regions: a center region and an edge region with different acoustic velocity characteristics. This segmentation allows independent optimization of each region's acoustic properties. The edge region is further segmented into specific crystal orientation zones to achieve the desired acoustic velocity profile, reducing spurious through localized structural design rather than complex overall structure.
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 in both the X and Y directions, improving the resonance characteristics and making it feasible to form the additional films, even at higher resonant frequencies, thereby enhancing the device's performance.
Implementation Method 1
a pair of electrodes sandwiching the piezoelectric substrate and exciting a thickness shear vibration in the piezoelectric substrate
Data Source
AI summary
An acoustic wave device includes: a piezoelectric substrate; electrodes sandwiching the piezoelectric substrate and exciting a thickness shear vibration in the piezoelectric substrate; and an edge region that is a region surrounding a center region of a resonance region, wherein a first region of the edge region is located on both sides of the center region in a first direction substantially parallel to a displacement direction of a thickness shear vibration, a second region of the edge region is located on both sides of the center region in a second direction substantially perpendicular to the first direction, a width of the second region is different from a width of the first region, and acoustic velocities of acoustic waves in the piezoelectric substrate in the first and second regions are less than that in the piezoelectric substrate in the center region.