Bulk Acoustic Resonator Electrode Layout for High-Q Filtering
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Solution Overview
Problem
Existing acoustic wave devices face challenges in downsizing while maintaining a high Q value and reducing spurious in filter characteristics.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer made of lithium niobate or lithium tantalate, with a configuration that includes pairs of electrodes opposed in a direction intersecting with the thickness direction of the piezoelectric layer. This configuration utilizes bulk waves in a thickness shear primary mode or sets the d/p ratio to about 0.5 or lower, with electrode orientations inclined at specific angles to reduce spurious and enhance filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the number of electrode fingers is reduced to downsize the acoustic wave device, then the device size is reduced, but the Q value decreases
Solution Approach 1:
The patent changes the wave propagation mode from surface waves to bulk waves in thickness shear mode, and optimizes the d/p ratio parameter to 0.5 or lower, enabling downsizing while maintaining high Q value through fundamental parameter changes in wave physics
Solution Approach 2:
The patent transitions from two-dimensional surface wave propagation to three-dimensional bulk wave propagation in the thickness direction, utilizing the thickness shear mode to achieve compact device design without compromising Q value
2Adaptability or versatility
If multiple acoustic wave resonators are used to configure a band pass filter, then filter functionality is achieved, but spurious is generated in other than main mode degrading filter characteristics
Solution Approach 1:
The patent changes the operating mode to bulk waves in thickness shear mode and sets specific electrode orientation angles, which fundamentally alters the wave propagation characteristics to suppress spurious generation while maintaining filter functionality
Solution Approach 2:
The patent introduces asymmetric electrode orientations where the direction orthogonal to the longitudinal direction of the second electrodes is inclined at an angle greater than 0° and smaller than 360° with respect to the first electrodes, creating directional selectivity that suppresses spurious modes
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
The proposed configuration effectively increases the Q value even during downsizing and reduces spurious in filter characteristics, thereby improving the overall performance of the acoustic wave device.
Implementation Method 1
an acoustic wave device includes a piezoelectric layer made of lithium niobate or lithium tantalate... in which a bulk wave in a thickness shear primary mode is used
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer that is made of lithium niobate or lithium tantalate, and a plurality of pairs of electrodes opposed to each other in a direction intersecting with a thickness direction of the piezoelectric layer, in which a bulk wave in a thickness shear primary mode is used or d/p is about 0.5 or lower when a thickness of the piezoelectric layer is d and a distance between centers of mutually adjacent electrodes among the plurality of pairs of electrodes is p. The plurality of pairs of electrodes include at least one pair of first electrodes of a first acoustic wave resonator and at least one pair of second electrodes of a second acoustic wave resonator. A direction orthogonal to a longitudinal direction of the second electrodes in the second acoustic wave resonator is inclined at an angle that is greater than 0° and smaller than 360° with respect to a direction orthogonal to a longitudinal direction of the first electrodes in the first acoustic wave resonator.