Acoustic Coupling Filter Electrode Nesting for Compact Resonators
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Solution Overview
Problem
Existing acoustic wave devices using bulk waves in a thickness shear mode face challenges in reducing the size of filter devices while maintaining satisfactory filter characteristics.
Innovation Solution
The acoustic wave device incorporates a configuration where a third electrode connected to a reference potential is disposed between electrodes connected to input and output potentials, and includes a piezoelectric film with a plurality of acoustic elements sharing a support, allowing for a reduction in size and prevention of filter characteristic deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the electrostatic capacitance of acoustic wave resonators is increased by enlarging their size, then the electrostatic capacitance ratio between resonators is improved, but the overall size of the filter device increases
Solution Approach 1:
The patent introduces a third electrode arranged in the depth direction (thickness direction of piezoelectric layer) rather than only in the planar direction. This dimensional transition allows increasing electrostatic capacitance by utilizing the thickness dimension, thereby reducing the need to enlarge the filter device in the plane direction while achieving the required capacitance ratio between resonators
Solution Approach 2:
The third electrode is positioned between the first and second electrodes in the depth direction, creating a nested electrode structure. This nested configuration allows multiple electrodes to occupy overlapping projection areas, effectively increasing capacitance without increasing the planar footprint of the device
2Adaptability or versatility
If another acoustic element is added to the filter device together with the acoustic wave resonator, then the filter functionality is improved, but the filter characteristic may deteriorate due to wave interference
Solution Approach 1:
The patent extracts and eliminates unnecessary acoustic waves generated by the acoustic coupling filter through careful design of the electrode configuration and acoustic element arrangement. By removing these harmful wave components, the filter characteristic is maintained even when multiple acoustic elements are integrated in the same device
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 a reduction in the size of filter devices and maintains or improves filter characteristics by effectively coupling acoustic waves and reducing unnecessary wave propagation.
Implementation Method 1
A piezoelectric layer is provided on a support body. A pair of electrodes are provided on the piezoelectric layer. An alternating current (AC) voltage is applied between the electrodes to excite the bulk wave in the thickness shear mode.
Implementation Method 2
a plurality of acoustic elements sharing a support, and a piezoelectric film that is provided on the support and includes a piezoelectric layer including a piezoelectric body
Data Source
AI summary
An acoustic wave device includes acoustic elements sharing a support, and a piezoelectric film on the support and including a piezoelectric layer that includes a piezoelectric body. The acoustic elements include a first acoustic element that is an acoustic coupling filter, and a second acoustic element electrically connected to the first acoustic element. In plan view, an acoustic reflection portion is provided in the support overlapping with first electrode fingers, second electrode fingers, and third electrode fingers of the first acoustic element and a functional electrode of the second acoustic element.