Acoustic Wave Filter Film Layout for Compact High-Q Tuning
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Solution Overview
Problem
Existing acoustic wave devices using piezoelectric films face challenges in maintaining a high Q value and adjusting frequency while reducing size, as decreasing the number of electrode fingers leads to propagation loss and reduced Q value.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer made of lithium niobate or lithium tantalate with additional films on the electrodes or the piezoelectric layer, utilizing primary thickness-shear mode bulk waves and optimizing the thickness and spacing of electrodes to maintain high Q values and allow for easy frequency adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the number of electrode fingers is reduced to decrease device size, then the device size is reduced, but the Q value decreases and frequency adjustment becomes difficult
Solution Approach 1:
The patent changes the wave propagation mode from plate waves (Lamb waves) to primary thickness-shear mode bulk waves, and optimizes the electrode spacing parameter (d/p ratio) to maintain high Q values in compact devices. This parameter change allows the device to achieve high Q values with fewer electrode fingers, resolving the contradiction between size reduction and Q value maintenance.
Solution Approach 2:
The patent transitions from two-dimensional plate wave propagation to three-dimensional bulk wave propagation in the thickness direction. This dimensional change enables effective energy confinement within the piezoelectric layer, reducing propagation loss and maintaining high Q values even when the device size is reduced in the planar direction.
2Volume of moving object
If the number of electrode fingers is reduced to decrease device size, then the device size is reduced, but frequency adjustment becomes difficult
Solution Approach 1:
The patent optimizes the d/p ratio (electrode thickness to center-to-center spacing) to be equal to or less than about 0.5, which enables effective excitation of primary thickness-shear mode bulk waves. This parameter optimization allows frequency adjustment through electrode spacing control while maintaining compact device size, resolving the contradiction between size reduction and frequency adjustability.
3Volume of moving object
If electrode fingers are reduced for size reduction, then device size decreases, but propagation loss increases
Solution Approach 1:
The patent transitions from two-dimensional plate wave propagation to three-dimensional bulk wave propagation, confining acoustic energy within the piezoelectric layer thickness. This dimensional change creates effective acoustic confinement that reduces energy leakage and propagation loss, enabling size reduction without significant Q value degradation.
Solution Approach 2:
By optimizing the d/p ratio and using primary thickness-shear mode bulk waves, the patent achieves more efficient energy confinement in the vertical direction. This parameter optimization reduces the number of electrode fingers needed for effective excitation, thereby reducing device size while maintaining low propagation loss through improved energy confinement.
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 confines energy within the excitation region, minimizing propagation loss and allowing for size reduction without significant Q value degradation, while enabling easy frequency adjustment through the additional film's thickness.
Implementation Method 1
The piezoelectric layer is made of lithium niobate or lithium tantalate... uses primary thickness-shear mode bulk waves
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer, at least one pair of electrodes adjacent to each other, and an additional film. The piezoelectric layer is made of lithium niobate or lithium tantalate, and includes first and second opposing principal surfaces. The at least one pair of electrodes is located on the first principal surface of the piezoelectric layer. The additional film is located on the piezoelectric layer or either one or both of the electrodes so as to overlap, in plan view, either one or both of areas in which the electrodes are located and an area between the electrodes. When d represents a thickness of the piezoelectric layer and p represents a center-to-center distance between the electrodes, d/p is equal to or less than about 0.5.