Acoustic Wave Filter Layout Using Asymmetric Reflection Gratings
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Solution Overview
Problem
Traditional surface acoustic wave (SAW) filters based on piezoelectric materials suffer from low operating frequency, high insertion loss, and strong fluctuations in the passband due to spurious waves, which are typically suppressed by increasing the thickness of the piezoelectric thin film, thereby compromising the overall performance of the filter.
Innovation Solution
The proposed structure of an acoustic wave filter incorporates cascaded parallel and series resonators, where the parallel resonators have a reduced number of reflection gratings and a subwavelength thickness piezoelectric thin film, while the series resonators have an increased number of reflection gratings, optimizing the Q value and suppressing spurious waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the thickness of the piezoelectric thin film is increased to suppress spurious waves, then the spurious wave is suppressed, but the operating frequency decreases and insertion loss increases
Solution Approach 1:
The patent applies different quantities of reflection gratings to different types of resonators within the same filter system. Parallel resonators use a first quantity (e.g., 2-4 pairs) while series resonators use a second quantity (e.g., 6-10 pairs), allowing each resonator type to have optimized local characteristics for its specific function while maintaining overall system performance
Solution Approach 2:
The patent changes the key parameter of reflection grating quantity to suppress spurious waves. By optimizing the number of reflection grating pairs rather than increasing piezoelectric film thickness, the patent achieves spurious wave suppression while maintaining high operating frequency and low insertion loss
2Object-affected harmful factors
If the thickness of the piezoelectric thin film is increased to suppress spurious waves, then the spurious wave is suppressed, but the bandwidth decreases
Solution Approach 1:
The patent implements local optimization by assigning different reflection grating quantities to parallel and series resonators based on their specific functional requirements, allowing the filter to achieve both spurious wave suppression and wide bandwidth through differentiated local configurations
Solution Approach 2:
The patent uses parameter optimization (reflection grating quantity) rather than parameter increase (film thickness) to achieve spurious wave suppression, thereby preserving the filter's bandwidth and overall performance characteristics
3Stability of the object's composition
If the quantity of reflection gratings is reduced in parallel resonators, then the spurious wave mode is suppressed and passband is stabilized, but the Q value decreases
Solution Approach 1:
The patent creates an asymmetric configuration where parallel resonators have fewer reflection gratings (optimized for passband stability) while series resonators have more reflection gratings (optimized for high Q value). This asymmetric distribution allows each resonator type to be optimized for its specific role in the cascaded system
Solution Approach 2:
The patent combines parallel and series resonators in a cascaded configuration, where the strengths of one resonator type compensate for the weaknesses of the other. The series resonators with higher Q values compensate for the lower Q value of parallel resonators, while the parallel resonators provide stable passband characteristics
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 effectively suppresses spurious wave modes, stabilizes the passband, and maintains high filter performance by compensating for the reduced Q value of parallel resonators with the increased Q value of series resonators, while ensuring low insertion loss.
Implementation Method 1
an acoustic wave filter includes: parallel resonators and series resonators, where the parallel resonators and the series resonators are cascaded; each of the parallel resonators includes a first supporting substrate, a first piezoelectric thin film, and a first electrode array
Implementation Method 2
A surface acoustic wave (SAW) filter is an important branch technology of the acoustic wave filter
Data Source
AI summary
A structure of an acoustic wave filter includes: parallel resonators and series resonators, where the parallel resonators and the series resonators are cascaded; each of the parallel resonators includes a first supporting substrate, a first piezoelectric thin film, and a first electrode array; the first piezoelectric thin film is disposed on the first supporting substrate, and the first electrode array is disposed on the first piezoelectric thin film; the first electrode array includes a first interdigital electrode array and a first reflection grating array; and a quantity of pairs of first reflection gratings of at least one of the parallel resonators is less than or equal to a first preset threshold, and the first preset threshold is less than 5. The present disclosure can effectively suppress a fluctuation in a passband while ensuring high performance of the filter.