Coupled-Cavity SAW Filter Structure for Compact Thermal Stability
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Solution Overview
Problem
Surface acoustic wave (SAW) filter devices face challenges with compactness and performance due to the sensitivity to temperature and weak electromechanical coupling of traditional piezoelectric substrates, leading to suboptimal pass-band characteristics and large footprints in existing filter structures.
Innovation Solution
A coupled cavity filter structure using a composite substrate with a piezoelectric layer and inter-digitated comb electrodes, allowing for guided shear or longitudinal waves, which enhances electromechanical coupling and reduces footprint by adjusting passband and using multiple reflecting structures to narrow the transition band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional piezoelectric substrates (monolithic Quartz, LiNbO3, or LiTaO3) are used, then the device can be manufactured with existing processes, but the filter performance deteriorates due to high temperature sensitivity or weak electromechanical coupling
Solution Approach 1:
The patent employs a composite substrate structure consisting of a piezoelectric layer deposited on a non-piezoelectric carrier substrate. This composite approach allows combining the beneficial properties of different materials: the piezoelectric layer provides necessary electromechanical coupling while the carrier substrate offers thermal stability and mechanical support, thereby resolving the contradiction between manufacturability and filter performance
Solution Approach 2:
The patent changes the fundamental parameter of substrate composition from monolithic to composite structure. By depositing a piezoelectric layer on a suitable carrier substrate, the system achieves optimized electromechanical coupling coefficients and reduced temperature sensitivity, directly improving filter performance while avoiding the harmful effects of traditional single-material substrates
2Ease of operation
If classical filter structures are used in SAW devices, then the device can be implemented with conventional designs, but the footprint increases and compactness decreases
Solution Approach 1:
The patent merges multiple filter functions into a single integrated SAW device structure. By combining the piezoelectric layer, interdigitated transducers, and resonant cavities in a unified composite substrate architecture, the design achieves compactness while maintaining all necessary filtering functions, thereby reducing the overall device footprint
Solution Approach 2:
The patent utilizes the vertical dimension by depositing a piezoelectric layer on top of a carrier substrate, creating a three-dimensional integrated structure. This vertical integration allows multiple functional elements to be stacked rather than laid out horizontally, significantly reducing the device footprint while maintaining compactness
3Reliability
If three kinds of architectures (SAW-ladder, LCRF, or DMS filters) are used, then the filter function can be achieved, but two or more poles must be placed in the passband resulting in non-optimized performance and larger footprint
Solution Approach 1:
The patent extracts and eliminates unnecessary structural elements from conventional filter architectures. By using the composite substrate with optimized piezoelectric layer and interdigitated transducers, the design achieves the required filter function with fewer poles and simpler structure, removing the need for multiple poles in the passband and reducing overall device complexity
Solution Approach 2:
The patent changes key parameters including electromechanical coupling coefficient and resonant frequency by optimizing the piezoelectric layer properties and transducer geometry. These parameter optimizations enable achieving superior filter performance with reduced structural complexity, avoiding the need for complex multi-pole architectures
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 solution achieves improved compactness, simplicity, and performance by optimizing filter structures with higher electromechanical coupling, reduced insertion loss, and sharper transition bands, while maintaining thermal stability.
Implementation Method 1
The acoustic wave propagation substrate is a composite substrate comprising a base substrate and a piezoelectric layer
Implementation Method 2
at least one input transducer structure and one output transducer structure, provided over the substrate, each comprising inter-digitated comb electrodes
Implementation Method 3
at least one reflecting structure, the at least one reflecting structure comprising at least one or more metallic strips, positioned at a distance d and in between the input and output transducer structures
Data Source
AI summary
A coupled cavity filter structure that uses a surface acoustic wave, in particular, a guided surface acoustic wave, comprises an acoustic wave propagating substrate, at least one input transducer structure and one output transducer structure, provided over the substrate, each comprising inter-digitated comb electrodes, at least one reflecting structure comprising at least one or more metallic strips positioned at a distance and in between the input and output transducer structures, in the direction of propagation of an acoustic wave. The acoustic wave propagating substrate is a composite substrate comprising a base substrate and a piezoelectric layer. In additional embodiments, a coupled cavity filter structure comprises a groove. In additional embodiments, a SAW ladder filter device comprises at least two coupled cavity filter structures as described herein, wherein the at least two coupled cavity filter structures are positioned on a single line.