Acoustic Wave Filter Layout for Spurious Emission Suppression
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Solution Overview
Problem
Spurious emissions are generated due to leakage of acoustic waves from the regions between comb-shaped electrodes and reflectors in acoustic wave devices, which affect the performance and efficiency of high-frequency communication systems.
Innovation Solution
An acoustic wave device is designed with an additional film between the comb-shaped electrodes and reflectors, where the overlap width and distance between the additional film and these components are controlled to be equal to or less than ⅛ of the average pitch of the electrode fingers, and the acoustic velocity of the lateral wave is adjusted to be within a specific range relative to the velocity in other regions, using materials like tantalum oxide or niobium oxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If first dielectric films covering the reflectors are provided to reduce device size, then the device size is reduced, but spurious emissions are generated due to acoustic wave leakage
Solution Approach 1:
An additional dielectric film is introduced as an intermediary element between the comb-shaped electrodes and the reflectors. This intermediate film serves as a mediator to suppress acoustic wave leakage while maintaining the compact device structure, thereby reducing spurious emissions without increasing device size
Solution Approach 2:
The acoustic velocity in the region between the comb-shaped electrodes and reflectors is modified by changing the dielectric constant of the additional dielectric film. By adjusting this parameter, the lateral wave propagation is controlled to match the main propagation region, minimizing spurious emissions while maintaining compact dimensions
2Object-generated harmful factors
If the overlap width and distance of the additional film are minimized to reduce spurious emissions, then spurious emissions are reduced, but manufacturing precision requirements increase
Solution Approach 1:
By optimizing the thickness and dielectric constant of the additional dielectric film, the design achieves effective spurious emission suppression with relaxed dimensional tolerances. The parameter optimization allows the overlap width and distance to be controlled within practical manufacturing capabilities while maintaining performance
3Object-generated harmful factors
If the acoustic velocity of lateral wave is adjusted to match the main propagation region, then spurious emissions are reduced, but device complexity increases
Solution Approach 1:
The additional dielectric film is selectively positioned only in the region between the comb-shaped electrodes and the reflectors, where spurious emissions occur. This localized modification changes the acoustic velocity only where needed, achieving spurious emission suppression without requiring complex modifications throughout the entire device 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 reduces spurious emissions by minimizing the difference in acoustic velocity across different regions, thereby enhancing the device's performance and reducing longitudinal-mode spurious emissions.
Implementation Method 1
an acoustic velocity of a lateral wave propagating through a region between the pair of comb-shaped electrodes and the reflector being equal to or greater than 0.95 times and equal to or less than 1.05 times an acoustic velocity of a lateral wave propagating through a region where the pair of comb-shaped electrodes are provided
Implementation Method 2
a piezoelectric body; a pair of comb-shaped electrodes provided on the piezoelectric body
Data Source
AI summary
An acoustic wave device includes a piezoelectric body, a pair of comb-shaped electrodes provided on the piezoelectric body, the pair of comb-shaped electrodes including a plurality of electrode fingers, a reflector provided on the piezoelectric body so as to be arranged in line with the pair of comb-shaped electrodes in an arrangement direction of the electrode fingers, and an additional film provided on the piezoelectric body between the pair of comb-shaped electrodes and the reflector so that an overlap width with the pair of comb-shaped electrodes and an overlap width with the reflector are equal to or less than ⅛ of an average pitch of the electrode fingers of the pair of comb-shaped electrodes and a distance between the additional film and the pair of comb-shaped electrodes and a distance between the additional film and the reflector are equal to or less than ⅛ of the average pitch.