Multi-Band Piezoelectric Filter with Band-Specific SH Wave Suppression
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Solution Overview
Problem
Existing multi-band filters face challenges in suppressing shear horizontal (SH) wave propagation, which degrades performance, particularly when fabricated on a single substrate, and existing methods like adjusting the cut angle of the substrate may not sufficiently address this issue across all targeted frequency bands.
Innovation Solution
A multi-band filter design that incorporates a piezoelectric substrate with a cut angle optimized for overall performance and utilizes varying thicknesses of a passivation film, specifically silicon nitride (SiN), tailored for each frequency band to suppress SH waves, with different thicknesses for different groups of electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single substrate is used for multi-band filter fabrication, then manufacturing complexity is reduced, but shear horizontal wave propagation cannot be sufficiently suppressed across all frequency bands
Solution Approach 1:
The patent applies local quality by varying the passivation film thickness at different locations corresponding to different frequency bands. Specifically, the passivation film has a first thickness for a first frequency band and a second thickness for a second frequency band, allowing each band to have optimized SH wave suppression while using a single substrate.
Solution Approach 2:
The patent changes the thickness parameter of the passivation film to suppress SH waves at different frequency bands. By adjusting the passivation film thickness to different values (first thickness and second thickness) for different frequency bands, the patent achieves effective SH wave suppression across multiple bands without requiring multiple substrates.
2Reliability
If passivation film thickness is varied for different frequency bands, then SH wave suppression is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements local quality by defining specific thickness regions for the passivation film corresponding to different frequency bands. The passivation film has a first thickness for a first frequency band and a second thickness for a second frequency band, allowing differentiated SH wave suppression while maintaining manufacturability through clear regional specifications.
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 design effectively suppresses SH wave propagation, enhancing the filter's performance across multiple frequency bands by optimizing the passivation film thickness based on the frequency band and electrode materials, thereby improving power delivery and reducing spurious responses.
Implementation Method 1
a piezoelectric substrate; a plurality of groups of electrodes disposed on the piezoelectric substrate
Implementation Method 2
a passivation film disposed on the dielectric film, the passivation film having a smaller thickness for the first group than for the second group, so as to suppress a spurious response generated in the piezoelectric substrate
Data Source
AI summary
A multi-band filter configured to allow signals to pass at multiple frequency bands includes a piezoelectric substrate and a plurality of groups of electrodes disposed on the piezoelectric substrate. Each group forms a respective filter to allow signals to pass at a corresponding frequency band. A first group forms a first filter having a first frequency band and a second group forms a second filter having a second frequency band. The first frequency band is lower than the second frequency band. The filter includes a dielectric film formed to cover at least a part of the piezoelectric substrate and the plurality of groups of electrodes. The filter also includes a passivation film disposed on the dielectric film. The passivation film has a smaller thickness for the first group than for the second group, so as to suppress a spurious response generated in the piezoelectric substrate.