Multi-Band Piezoelectric Filter Using Local Passivation Thickness
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Solution Overview
Problem
Existing multi-band filters face issues with spurious shear horizontal (SH) wave propagation, which degrades performance, particularly when implemented on a single substrate, and there is a need to suppress this mode for improved filter performance in radio frequency communication systems.
Innovation Solution
The multi-band filter design incorporates a piezoelectric substrate with a specific cut angle and varying thicknesses of the passivation film for different frequency bands, using materials like silicon nitride (SiN) and silicon dioxide (SiO2) to suppress SH wave propagation, with each group of electrodes having distinct upper and lower portions made of metals such as aluminum (Al), aluminum-magnesium-copper (AlMgCu) alloy, tungsten (W), platinum (Pt), and molybdenum (Mo).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a multi-band filter is implemented on a single piezoelectric substrate, then device integration and compactness are improved, but spurious shear horizontal wave propagation occurs degrading filter performance
Solution Approach 1:
The patent applies local quality by varying the passivation film thickness locally over different regions of the piezoelectric substrate. Specifically, the passivation film has a first thickness in a first region and a second thickness in a second region, where the thickness ratio between these regions is configured to suppress spurious SH wave propagation while maintaining compact multi-band filter functionality on a single substrate.
2Ease of manufacture
If uniform passivation film thickness is used across all frequency bands, then manufacturing simplicity is improved, but spurious response suppression is insufficient
Solution Approach 1:
The patent implements local quality by configuring the passivation film with different thicknesses in different regions corresponding to different frequency bands. The passivation film thickness ratio between the first region and second region is specifically designed to suppress spurious SH wave responses, thereby eliminating harmful effects while maintaining manufacturing feasibility through a single film deposition process with spatially varying thickness.
3Reliability
If passivation film thickness is increased to suppress spurious waves, then filter performance is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent applies parameter changes by optimizing the passivation film thickness ratio rather than uniformly increasing thickness throughout. By configuring specific thickness ratios between different regions, the patent achieves effective spurious wave suppression while avoiding the need for multiple passivation layers or complex structural modifications, thus improving performance without proportionally increasing device complexity.
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 design effectively suppresses SH wave propagation across multiple frequency bands, enhancing output power delivery and filter performance by optimizing the passivation film thickness and material selection based on frequency bands, thereby improving overall filter efficiency.
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.