Acoustic Wave Resonator IDT Layout for Lateral-Mode Suppression
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Solution Overview
Problem
Acoustic wave resonators in high-frequency communication systems suffer from lateral-mode spurious signals due to acoustic waves propagating in directions perpendicular to the main propagation direction, leading to energy leakage and increased loss.
Innovation Solution
The design incorporates an Interdigital Transducer (IDT) with comb-shaped electrodes on a piezoelectric substrate, where the anisotropy coefficient in the overlap region is positive, and in the gap region between the electrodes and bus bar, it is less than in the overlap region, ensuring the acoustic velocity in the gap region is equal to or less than in the overlap region at antiresonant frequency, thereby reducing lateral-mode spurious signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the cross width of the grating electrode is varied to reduce lateral-mode spurious, then the frequency averaging effect reduces spurious signals, but acoustic wave energy still leaks to the outside causing loss
Solution Approach 1:
The patent applies local quality by creating different anisotropy coefficients in different regions (overlap region vs gap region) of the IDT structure. The overlap region has a positive anisotropy coefficient while the gap region has a lower anisotropy coefficient, causing acoustic waves to be reflected at the boundary and preventing energy leakage to the bus bar, thus resolving both the spurious signal and energy loss issues
Solution Approach 2:
The patent implements preliminary anti-action by designing the anisotropy coefficient distribution in advance to prevent acoustic wave leakage before it occurs. The boundary between the overlap region and gap region is engineered to reflect acoustic waves back into the overlap region, preventing them from reaching the bus bar and causing energy loss or spurious signals
2Productivity
If a metal grating electrode is formed on a piezoelectric substrate to create acoustic wave resonators, then high-frequency filtering is achieved, but lateral-mode spurious signals occur due to perpendicular acoustic wave propagation
Solution Approach 1:
The patent maintains the metal grating electrode structure for high-frequency filtering while introducing local quality variations through different anisotropy coefficients in the overlap and gap regions. This allows the IDT to maintain its filtering capability while the regional differences prevent lateral-mode spurious by reflecting perpendicular acoustic waves at the region boundary
3Reliability
If the anisotropy coefficient in the gap region is made less than in the overlap region, then acoustic wave reflection is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses parameter changes by adjusting the anisotropy coefficient values in different regions to achieve acoustic wave reflection. By setting the overlap region with a positive anisotropy coefficient and the gap region with a lower anisotropy coefficient, the design creates a natural boundary for wave reflection that can be controlled through material selection and geometric parameters rather than requiring extreme manufacturing precision
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 inhibits the generation and leakage of lateral-mode spurious signals, reducing energy loss and increasing the Q-value of the acoustic wave resonator.
Implementation Method 1
The grating electrode excites a Shear Horizontal (SH) wave, a Rayleigh wave, or a boundary acoustic wave, which is a type of surface acoustic waves
Implementation Method 2
a piezoelectric substrate; and an Interdigital Transducer (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 including a grating electrode that excites an acoustic wave
Data Source
AI summary
An acoustic wave resonator includes: a piezoelectric substrate; and an IDT located on the piezoelectric substrate and including a pair of comb-shaped electrodes facing each other, each of the pair of comb-shaped electrodes including a grating electrode exciting an acoustic wave and a bus bar to which the grating electrode is connected, wherein an anisotropy coefficient in a cross region where the grating electrodes of the pair of comb-shaped electrodes cross each other is positive; an anisotropy coefficient in a gap region located between a tip of the grating electrode of one of the pair of comb-shaped electrodes and the bus bar of the other is less than the anisotropy coefficient in the cross region, and an acoustic velocity of an acoustic wave propagating through the gap region is equal to or less than an acoustic velocity of an acoustic wave propagating through the cross region at an antiresonant frequency.