Acoustic Wave Filter Duty Factor Tuning for Temperature Stability
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Solution Overview
Problem
Existing acoustic wave filters exhibit degraded attenuation and temperature instability due to a positive temperature coefficient of frequency (TCF) for resonant frequencies, leading to a lower slope at the edge of the band, especially at low temperatures.
Innovation Solution
The implementation of acoustic filter devices with series and parallel resonators, where some resonators are covered with negative or positive TCF materials and others are uncovered, and interdigital transducers with varying duty factors to synchronize the TCF values of resonant and anti-resonant frequencies, improving temperature stability and rejection performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all resonators are uncovered or uniformly covered with the same TCF material, then the manufacturing process is simple, but the temperature stability and rejection performance are degraded due to positive TCF at resonant frequencies
Solution Approach 1:
The patent applies local quality by differentiating the treatment of series and parallel resonators. Series resonators are covered with a first TCF material (or left uncovered) while parallel resonators are covered with a second TCF material (or left uncovered), creating locally optimized TCF characteristics for each resonator type to achieve overall temperature stability
Solution Approach 2:
The patent segments the resonator group into series resonators and parallel resonators with different TCF configurations. This segmentation allows independent optimization of each group's temperature response, enabling the composite filter to achieve zero TCF at both resonant and anti-resonant frequencies
2Reliability
If the TCF values of resonant and anti-resonant frequencies are not synchronized, then the device structure is simple, but the attenuation performance is degraded with lower slope at band edges
Solution Approach 1:
The patent changes the TCF parameter by selectively applying different TCF materials to series and parallel resonators. This parameter modification synchronizes the TCF values at resonant and anti-resonant frequencies, optimizing the attenuation characteristics and slope at band edges
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 enhances temperature stability and rejection performance by synchronizing the TCF values of resonant and anti-resonant frequencies, resulting in improved attenuation across a wide band pass filter.
Implementation Method 1
some resonators are covered with negative or positive TCF materials and others are uncovered, and interdigital transducers with varying duty factors to synchronize the TCF values of resonant and anti-resonant frequencies, improving temperature stability
Implementation Method 2
A piezoelectric layer is disposed over the substrate. A first plurality of acoustic wave resonators is disposed over the piezoelectric layer
Data Source
AI summary
An acoustic wave filter includes a substrate and a piezoelectric layer over the substrate. First acoustic wave resonators are disposed over the piezoelectric layer and arranged in series along a first branch, and second acoustic wave resonators are disposed over the piezoelectric layer, arranged in parallel, and connected to the first branch and to ground. The first and second acoustic wave resonators include an interdigital transducer electrode interposed between a pair of reflectors. The interdigital transducer electrode of one or more of the second plurality of acoustic wave resonators has a wider duty factor than the interdigital transducer electrodes of the first plurality of acoustic wave resonators.