Piston-Mode Lamb Wave Resonator Layout for Transverse Mode Suppression
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Solution Overview
Problem
Piezoelectric MEMS resonators, specifically aluminum nitride Lamb wave resonators, face challenges with strong transverse modes that hinder the accuracy and stability of oscillators and acoustic filters by causing passband ripples and limiting signal rejection, due to their multimode behavior and high transduction efficiency.
Innovation Solution
The introduction of a piston mode Lamb wave resonator with a border region having a lower velocity than the active region, designed to suppress transverse modes by modifying the interdigital transducer layout and metal coverage ratio, effectively canceling out transverse wave vectors and maintaining high transduction efficiency without introducing acoustic loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum nitride Lamb wave resonators are used for their high transduction efficiency, then signal processing capability is improved, but transverse modes are strongly excited causing passband ripples and limiting signal rejection
Solution Approach 1:
The patent applies local quality by creating a border region with different material composition and acoustic properties than the active region. Specifically, the border region has reduced metal coverage ratio or different dielectric material, resulting in lower acoustic velocity compared to the active region. This local variation in properties enables selective suppression of transverse modes while maintaining Lamb wave operation in the active region.
Solution Approach 2:
The resonator structure is segmented into distinct functional regions: an active region for Lamb wave generation and a border region for transverse mode suppression. This segmentation allows independent optimization of each region's properties, enabling the active region to maintain high transduction efficiency while the border region specifically targets transverse mode control through its distinct acoustic characteristics.
2Reliability
If the resonator operates in multimode behavior, then transduction efficiency is improved, but oscillator accuracy and stability are hindered
Solution Approach 1:
By implementing a border region with lower acoustic velocity adjacent to the active region, the patent creates a localized acoustic environment that selectively affects transverse modes. The velocity difference between the border region and active region causes transverse wave vectors to be canceled or suppressed, while the Lamb wave mode in the active region remains unaffected, thus maintaining oscillator stability without sacrificing transduction efficiency.
3Reliability
If a border region with lower velocity is introduced to suppress transverse modes, then transverse mode coupling is reduced, but device complexity increases
Solution Approach 1:
The border region can be implemented through simple geometric modifications such as varying the metal coverage ratio in the interdigital transducer pattern or applying different dielectric materials, rather than requiring completely separate structural components. This approach achieves transverse mode suppression through material and geometric parameter variation within the existing resonator architecture, minimizing additional complexity.
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
The piston mode Lamb wave resonator achieves spurious-free operation with high quality factor (Q) and effective electromechanical coupling coefficient (k2eff), enabling improved performance in filters and sensors by reducing transverse mode coupling and maintaining high frequency ability.
Implementation Method 1
Piezoelectric MEMS resonators can process electrical signals using mechanically vibrating structures
Implementation Method 2
The border region is configured to suppress a transverse mode
Implementation Method 3
The piston mode Lamb wave resonator is configured to generate a Lamb wave
Data Source
AI summary
Piston mode Lamb wave resonators are disclosed. A piston mode Lamb wave resonator can include a piezoelectric layer, such as an aluminum nitride layer, and an interdigital transducer on the piezoelectric layer. The piston mode Lamb wave resonator has an active region and a border region, in which the border region has a velocity with a lower magnitude than a velocity of the active region. The border region can suppress a transverse mode.