Acoustic Wave Resonator IDT Layout for Size and Spurious Control
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Solution Overview
Problem
Existing acoustic wave resonators face challenges in reducing size while maintaining input and output impedance, as increasing the duty ratio in the edge region to lower acoustic velocity is difficult without affecting the center region's duty ratio and increasing the complexity of fabrication.
Innovation Solution
The acoustic wave resonator design features a pair of comb-shaped electrodes with differing duty ratios and widths in the center and edge regions, allowing for a reduced size without altering the impedance, achieved by setting the duty ratio in the center region to 65% or greater and in the edge region to 50% or less, thereby reducing the resonator's size while maintaining the piston mode and reducing lateral-mode spurious.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the duty ratio in the edge region is increased to lower acoustic velocity, then lateral-mode spurious is reduced, but the fabrication complexity increases and the center region's duty ratio is affected
Solution Approach 1:
The patent applies local quality by differentiating the duty ratio settings between the center region and edge region of the IDT. The center region maintains a duty ratio of 65% or greater while the edge region uses 50% or less, allowing each region to have optimized properties for its specific function without affecting the other region's characteristics
Solution Approach 2:
The IDT is segmented into distinct center and edge regions with different duty ratio characteristics. This segmentation allows independent optimization of each region's acoustic velocity properties, enabling the edge region to reduce lateral-mode spurious while the center region maintains proper impedance characteristics
2Volume of moving object
If the resonator size is reduced, then the device becomes more compact, but maintaining the desired input and output impedance becomes difficult
Solution Approach 1:
The patent changes the duty ratio parameter differently in the center and edge regions to achieve both size reduction and impedance maintenance. By setting the center region duty ratio to 65% or greater, the electrostatic capacitance is optimized for proper impedance, while the overall resonator dimensions are reduced through the edge region's 50% or less duty ratio configuration
3Volume of moving object
If the duty ratio in the center region is increased to reduce resonator size, then the device becomes more compact, but the acoustic velocity distribution is affected
Solution Approach 1:
The patent ensures that the center region's high duty ratio (65% or greater) does not negatively affect acoustic velocity distribution by confining this high duty ratio setting specifically to the center region. The edge region's lower duty ratio (50% or less) compensates for any acoustic velocity issues, maintaining proper piston mode operation while allowing the center region to contribute to size 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 the size of the acoustic wave resonator while maintaining the desired impedance and achieving the piston mode, which reduces lateral-mode spurious, and simplifies the fabrication process by maintaining a larger interval between grating electrodes.
Implementation Method 1
an IDT that is located on the piezoelectric substrate and includes a pair of comb-shaped electrodes facing each other, each of the pair of comb-shaped electrodes having grating electrodes, which excite an acoustic wave
Data Source
AI summary
An acoustic wave resonator includes: a piezoelectric substrate; and an IDT that is located on the piezoelectric substrate and includes comb-shaped electrodes facing each other, each of the comb-shaped electrodes having grating electrode and a bus bar connected to the grating electrodes, a duty ratio of grating electrodes of the comb-shaped electrodes in a center region of an overlap region differing from a duty ratio of grating electrodes of the comb-shaped electrodes in an edge region of the overlap region in an arrangement direction of the grating electrodes, the grating electrodes of each of the comb-shaped electrodes overlapping with the grating electrodes of the other in the overlap region, a grating electrode of a first one of the comb-shaped electrodes in the center region having a different width from a grating electrode of a second one of the comb-shaped electrodes in the center region.