Coupled-Cavity SAW Filter Structure on Composite Substrates
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Solution Overview
Problem
Existing surface acoustic wave (SAW) filter devices face challenges with compactness, performance, and temperature sensitivity due to the use of monolithic piezoelectric substrates like Quartz, LiNbO3, or LiTaO3.
Innovation Solution
A coupled cavity filter structure using a composite substrate with a base substrate and a piezoelectric layer, incorporating inter-digitated comb electrodes, reflecting structures with metallic strips, and Bragg mirrors to achieve improved compactness and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If monolithic piezoelectric substrates (Quartz, LiNbO3, or LiTaO3) are used for SAW filter devices, then the device structure is simple and easy to manufacture, but the device exhibits high sensitivity to temperature or weak electromechanical coupling, resulting in poor pass-band characteristics
Solution Approach 1:
The patent employs a composite substrate structure consisting of a piezoelectric layer deposited on a non-piezoelectric base substrate (such as silicon). This composite approach combines the advantages of piezoelectric materials (strong electromechanical coupling for signal generation/detection) with the benefits of the base substrate (thermal stability, mechanical strength, and integration compatibility), thereby resolving the contradiction between manufacturing simplicity and performance reliability
Solution Approach 2:
The patent modifies the substrate parameters by transitioning from monolithic piezoelectric substrates to composite substrates with controlled layer thicknesses and material properties. By adjusting the piezoelectric layer thickness and selecting appropriate base substrates, the device achieves optimized electromechanical coupling and temperature stability, improving pass-band characteristics while maintaining manufacturing feasibility
2Device complexity
If classical filter structures are used in SAW devices, then the device design is straightforward, but the device footprint is large and compactness is poor
Solution Approach 1:
The patent transitions from planar two-dimensional filter structures to three-dimensional coupled cavity structures utilizing vertical acoustic wave propagation. By stacking multiple cavities in the vertical dimension and using through-silicon vias for inter-layer connections, the filter achieves complex filtering functionality in a compact volume, significantly reducing the device footprint while maintaining design systematicity
Solution Approach 2:
The patent implements nested cavity structures where multiple acoustic cavities are arranged in series, with each cavity containing resonant elements. The cavities are nested along the acoustic wave propagation path, allowing multiple filtering functions to be integrated in a compact sequence, thereby reducing the overall device area while maintaining design simplicity through modular repetition
3Ease of operation
If multiple poles are placed in the passband using conventional SAW filter architectures, then the filter function is achieved, but the device performance is non-optimized and the footprint is relatively large
Solution Approach 1:
The patent applies local quality optimization by placing resonant elements with specific properties at strategic locations within each cavity. Different cavity regions have locally optimized resonant element configurations (such as post structures, inter-digital transducers, or capacitive elements) tailored to achieve desired pole-zero placements, improving overall filter performance while reducing the number of cavities needed and thus the device footprint
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 proposed solution enables adjustment of the passband and reduces the footprint of SAW filter devices, while also providing enhanced electromechanical coupling and thermal compensation, leading to improved filter performance with reduced insertion loss and increased rejection.
Implementation Method 1
a piezoelectric layer... comprising a first substrate and a piezoelectric layer formed over the first substrate
Implementation Method 2
Bragg mirrors to achieve improved compactness and performance
Implementation Method 3
coupled cavity filter structure... incorporating inter-digitated comb electrodes, reflecting structures with metallic strips, and Bragg mirrors
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.