Acoustic Wave Resonator Structure for Transverse Mode Suppression
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Solution Overview
Problem
Existing acoustic wave devices struggle to reliably suppress transverse modes, which result in spurious responses and affect the performance of filters and resonators.
Innovation Solution
The acoustic wave device incorporates a high acoustic velocity material layer, a piezoelectric layer made of lithium tantalate or lithium niobate, and an interdigital transducer (IDT) with specific electrode finger configurations and mass addition films. The device is designed to optimize the Al-equivalent normalized thickness and thickness ratio of the mass addition film relative to the electrode finger portions, ensuring that the wavelength ratio width and thickness ratio fall within specific ranges defined by elliptical formulas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mass addition films are added to suppress transverse modes, then spurious response is reduced, but device structure becomes more complex
Solution Approach 1:
The patent applies local quality by positioning mass addition films specifically at edge regions of the IDT electrode rather than uniformly across the entire electrode. This localized approach suppresses transverse modes at the edges where they originate, while maintaining simpler structure in the central region. The selective placement optimizes spurious response suppression without unnecessarily complicating the overall device structure.
Solution Approach 2:
The IDT electrode is segmented into a central region and edge regions, with mass addition films applied only to the edge regions. This segmentation allows different parts of the electrode to have different characteristics - the central region maintains simple structure for efficient acoustic wave generation, while the edge regions have added mass for transverse mode suppression.
2Reliability
If mass addition film thickness is increased to improve transverse mode suppression, then spurious response decreases, but manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the thickness parameter of the mass addition film to achieve effective transverse mode suppression while maintaining manufacturability. By carefully selecting the thickness within a specific range, the design balances the suppression effectiveness with the practical constraints of film deposition processes, avoiding excessively thin films that would be difficult to control or too thick films that would be costly to manufacture.
3Reliability
If electrode finger dimensions are modified to suppress transverse modes, then spurious response is reduced, but device area increases
Solution Approach 1:
The patent modifies the electrode finger structure locally at the edge regions by adding mass addition films, rather than changing the dimensions of the entire electrode. This localized modification suppresses transverse modes without increasing the overall device area, as the changes are confined to specific regions rather than requiring uniform expansion of the entire IDT structure.
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 reduces or prevents transverse modes, leading to improved frequency characteristics with reduced ripples, thereby enhancing the performance and reliability of acoustic wave filters and resonators.
Implementation Method 1
a piezoelectric layer on the high acoustic velocity material layer and including lithium tantalate
Implementation Method 2
an acoustic velocity of a bulk wave that propagates in the high acoustic velocity material layer is higher than an acoustic velocity of an acoustic wave that propagates in the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a high acoustic velocity material layer, a piezoelectric layer including lithium tantalate, and an IDT on the piezoelectric layer and including electrode finger portions each including at least one electrode finger portion layer. An acoustic velocity of a bulk wave propagating in the high acoustic velocity material layer is higher than that in the piezoelectric layer. TR=(1/3.15)× (Tm/TIDT)×100 [%] is satisfied, where TR is a value obtained by dividing a thickness ratio of an Al-equivalent normalized thickness Tm of a mass addition film relative to an Al-equivalent normalized thickness TIDT of the electrode finger portion by about 3.15. A wavelength ratio width and a thickness ratio have values within a range on an ellipse and inside of the ellipse on an xy plane expressed by:x=0.19×cos(−5.5°)×cos θ−0.021×sin(−5.5°)×sin θ+0.0146×TIDT2−0.229×TIDT+1.5611+0.4×(d−0.55),andy=0.19×sin(−5.5°)×cos θ+0.021×cos(−5.5°)×sin θ+10.15.