Boundary Acoustic Wave Layer Stack for Thin Resonator Confinement
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Solution Overview
Problem
Boundary acoustic wave devices face challenges in confining acoustic waves and achieving thin device thickness, which affects their performance and packaging size.
Innovation Solution
A multi-layer piezoelectric device with high velocity layers on opposing sides of a piezoelectric layer and a low velocity layer between them, generating a boundary acoustic wave with improved confinement and reduced device height, using materials like silicon and silicon dioxide to enhance acoustic energy concentration and temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a boundary acoustic wave device is designed to confine acoustic waves, then acoustic energy concentration is improved, but device thickness increases
Solution Approach 1:
The patent transitions from traditional surface acoustic wave confinement to boundary acoustic wave confinement by changing the wave propagation dimension. The boundary acoustic wave propagates along the interface between the piezoelectric layer and substrate, confining energy in three dimensions (two horizontal, one vertical at the interface) rather than just along a surface, achieving better confinement with reduced thickness
Solution Approach 2:
The patent employs a composite layered structure consisting of a piezoelectric layer with specific acoustic velocity properties bonded to a substrate with different acoustic velocity properties. This composite structure creates the boundary acoustic wave mode that provides both confinement and thinness, leveraging the acoustic impedance contrast between materials
2Length of moving object
If the piezoelectric layer thickness is reduced to achieve a thinner device, then device compactness is improved, but acoustic energy confinement deteriorates
Solution Approach 1:
The invention changes the confinement mechanism from relying on sufficient piezoelectric layer thickness to relying on the boundary interface between layers. The boundary acoustic wave is confined at the interface between the piezoelectric layer and substrate, allowing thin piezoelectric layers while maintaining confinement through the acoustic velocity contrast at the boundary
3Device complexity
If traditional surface acoustic wave devices are used, then device simplicity is maintained, but radiation loss increases
Solution Approach 1:
The patent uses a composite structure of piezoelectric layer and substrate with contrasting acoustic velocities to create boundary acoustic wave confinement. This composite interface acts as an acoustic barrier that reduces radiation loss into the substrate while maintaining structural simplicity
Solution Approach 2:
By transitioning to boundary acoustic waves that propagate along the interface between layers rather than along the top surface, the invention naturally reduces radiation loss in the vertical direction into the substrate, as the boundary wave mode is confined by the acoustic velocity contrast
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 solution effectively confines acoustic energy within the device, allowing for a thinner, more compact design that maintains performance and reduces radiation loss, while also improving temperature stability and electromechanical coupling coefficients.
Implementation Method 1
A boundary acoustic wave resonator can include an interdigital transducer electrode on a piezoelectric substrate
Implementation Method 2
Boundary acoustic wave resonators can be implemented without a cavity over the surface of a chip that generates a boundary acoustic wave
Data Source
AI summary
Aspects of this disclosure relate to an acoustic wave device that includes high velocity layers on opposing sides of a piezoelectric layer. A temperature compensation layer can be positioned between one of the high velocity layers and the piezoelectric layer. The acoustic wave device can be arranged to generate a boundary acoustic wave having a higher velocity than a respective acoustic velocity of each of the high velocity layers.