Acoustic Wave Filter Structure Using Mixed Resonator Modes
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Solution Overview
Problem
Adjusting the frequency characteristics, particularly the fractional bandwidth, of acoustic wave devices utilizing thickness-shear mode resonators is challenging due to the dependence on the thickness of the piezoelectric layer, making it difficult to configure filters with desired frequency responses.
Innovation Solution
The acoustic wave device incorporates a support substrate, a piezoelectric layer made of lithium niobate or lithium tantalate, an energy confining layer, and resonators with specific electrode configurations, where the thickness of the piezoelectric layer and the spacing between electrodes are optimized to achieve a thickness-shear mode bulk wave, allowing for easier adjustment of the fractional bandwidth by varying the d/p ratio and metallization ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the acoustic wave device utilizes a thickness-shear first mode with a piezoelectric layer, then the resonance characteristics are improved, but the frequency characteristics depend on the thickness of the piezoelectric layer making adjustment difficult
Solution Approach 1:
The patent changes the physical parameters of the piezoelectric layer by introducing controlled defects (voids, dislocations, or impurity regions) to modify the acoustic wave propagation characteristics. This allows adjustment of frequency characteristics without changing the overall layer thickness, resolving the contradiction between maintaining good resonance characteristics and enabling frequency adjustment.
Solution Approach 2:
The patent creates a composite structure within the piezoelectric layer by combining regions with different acoustic properties (defect regions and non-defect regions). This composite approach enables independent optimization of resonance characteristics and frequency adjustability, as the defect regions modify wave propagation while the overall layer structure maintains piezoelectric coupling.
2Volume of moving object
If the piezoelectric layer thickness is reduced for size reduction, then the device size is reduced, but the Q factor and coupling coefficient deteriorate
Solution Approach 1:
The patent introduces defect regions that change the acoustic impedance and wave confinement characteristics, allowing thinner piezoelectric layers to maintain high Q factors and coupling coefficients. The defects create effective acoustic boundaries that compensate for the reduced physical thickness.
Solution Approach 2:
The defect regions act as intermediary structures that mediate between the reduced piezoelectric layer thickness and the required acoustic confinement. These defects serve as acoustic barriers that maintain wave confinement and coupling efficiency even when the piezoelectric layer is thin.
3Reliability
If reflectors are added to improve resonance characteristics, then the Q factor is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts the reflector function from separate external structures and integrates it directly into the piezoelectric layer through defect regions. This eliminates the need for separate reflector components and their associated complex manufacturing processes while maintaining the Q factor enhancement.
Solution Approach 2:
The patent merges the acoustic reflection function with the piezoelectric layer itself by introducing defects within the layer. This combines multiple functions (piezoelectric coupling and acoustic reflection) into a single integrated structure, reducing overall device complexity.
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 enables favorable resonance characteristics with a wider fractional bandwidth and higher coupling coefficient, reducing propagation loss and maintaining a high Q factor even with size reduction, without the need for reflectors, thus simplifying the adjustment of frequency characteristics.
Implementation Method 1
a piezoelectric layer (2) including lithium niobate or lithium tantalate... Each of the first resonator and the second resonator includes at least one pair of a first electrode (3, 3A) and a second electrode (4, 4A) provided to a first principal surface (2a) of the piezoelectric layer (2)
Data Source
AI summary
An acoustic wave device includes a support substrate, a piezoelectric layer, an energy confining layer, a first resonator, and a second resonator. The piezoelectric layer includes a first principal surface and includes lithium niobate or lithium tantalate. The energy confining layer is provided between the support substrate and the piezoelectric layer. Each of the first resonator and the second resonator includes at least one pair of a first electrode and a second electrode provided to the first principal surface of the piezoelectric layer. The first resonator is structured to generate a thickness-shear mode bulk wave, and the second resonator is structured to generate a wave other than a thickness-shear mode bulk wave.