Guided SAW Resonator Apodization Edges for Spurious Mode Control
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) resonators face challenges in reducing spurious modes while maintaining high quality factor, electromechanical coupling coefficient, and small size, as regular apodization degrades these performance metrics and requires increased device size.
Innovation Solution
The acoustic resonator features a piezoelectric layer with an interdigital electrode structure where the apodization edges are designed in a wave pattern, such as sinusoids, to reduce spurious modes while maintaining high quality factor and electromechanical coupling coefficient, and allowing for a smaller size due to increased capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If regular apodization is used to reduce spurious modes, then spurious modes are reduced, but quality factor and electromechanical coupling coefficient degrade and device size increases
Solution Approach 1:
The patent applies curvature by designing the apodization edges with a wave pattern (sinusoidal curves) instead of straight lines. This curved geometry modifies the acoustic wave distribution at the edges, reducing spurious modes while maintaining the desired resonator performance characteristics including quality factor and coupling coefficient.
Solution Approach 2:
The patent changes the geometric parameters of the apodization edges by introducing a wave pattern with specific amplitude and wavelength. This parameter modification allows the resonator to achieve reduced spurious modes while maintaining high quality factor and electromechanical coupling coefficient, resolving the technical contradiction.
2Object-generated harmful factors
If regular apodization is used to reduce spurious modes, then spurious modes are reduced, but device size increases
Solution Approach 1:
The wave pattern applied to the apodization edges creates a curved boundary that reduces spurious modes more effectively than straight edges. This curved geometry allows for compact resonator design by reducing the required aperture size while maintaining effective spurious mode suppression.
Solution Approach 2:
By optimizing the wave pattern parameters (amplitude, wavelength, and number of periods), the patent achieves effective spurious mode reduction within a smaller device footprint. The parameter optimization allows the resonator to maintain performance while reducing overall size.
3Object-generated harmful factors
If wave pattern apodization is used, then spurious modes are reduced and quality factor is maintained, but manufacturing complexity increases
Solution Approach 1:
The wave pattern can be implemented using standard photolithography techniques with appropriate mask design. The sinusoidal curves, while geometrically complex, can be fabricated using conventional semiconductor manufacturing processes, keeping manufacturing complexity manageable.
Solution Approach 2:
The wave pattern parameters can be optimized to balance performance and manufacturability. By selecting appropriate wavelengths and amplitudes that are multiples of the acoustic wavelength, the pattern becomes easier to fabricate while maintaining effective spurious mode reduction.
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 reduces spurious modes, enhances quality factor and electromechanical coupling coefficient, and enables a smaller device size by optimizing the apodization pattern, as demonstrated by improved performance graphs compared to conventional SAW resonators.
Implementation Method 1
Piezoelectric materials acquire a charge when compressed, twisted, or distorted, and similarly compress, twist, or distort when a charge is applied to them. Accordingly, when an alternating electrical signal is applied to the one or more electrodes in contact with the piezoelectric material, a corresponding mechanical signal (i.e., an oscillation or vibration) is transduced therein.
Implementation Method 2
surface acoustic wave (SAW) resonators
Data Source
AI summary
An acoustic resonator includes a piezoelectric layer on a substrate and an interdigital electrode structure on the piezoelectric layer. The interdigital electrode structure includes a first bus bar, a second bus bar, a first set of electrode fingers, and a second set of electrode fingers. The first bus bar and the second bus bar extend parallel to one another along a length of the interdigital electrode structure. The first set of electrode fingers are coupled to the first bus bar and extend to a first apodization edge. The second set of electrode fingers are coupled to the second bus bar and extend to a second apodization edge. The first set of electrode fingers and the second set of electrode fingers are interleaved. At least one of the first apodization edge and the second apodization edge provides a wave pattern along the length of the interdigital electrode structure.