SAW Device Composite Substrate with Uneven Interface
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Solution Overview
Problem
Surface acoustic wave devices using composite substrates with piezoelectric materials like lithium tantalate or lithium niobate face issues with temperature stability and spurious noise due to high thermal expansion coefficients and wave reflection at the interface between the piezoelectric crystal film and the support substrate.
Innovation Solution
A composite substrate with a piezoelectric single crystal substrate and a support substrate featuring an uneven structure at the interface, where the ratio of the average length of the uneven structure elements to the surface acoustic wave wavelength is between 0.2 and 7.0, and an intervening layer of materials like SiO2 or Al2O3, which helps reduce spurious noise and improve temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a piezoelectric single crystal substrate is bonded to a support substrate to improve temperature stability, then temperature characteristics are improved, but spurious noise occurs due to wave reflection at the joined interface
Solution Approach 1:
An intervening layer is introduced between the piezoelectric single crystal substrate and the support substrate at the joined interface. This intermediary layer reduces wave reflection and spurious noise while maintaining the temperature stability benefits of the composite substrate structure.
Solution Approach 2:
The joined interface is segmented into multiple layers including the piezoelectric substrate, an intervening layer, and the support substrate. This segmentation allows each layer to perform its specific function: the piezoelectric layer provides temperature stability, while the intervening layer reduces spurious noise through controlled acoustic impedance matching.
2Stability of the object's composition
If the piezoelectric substrate is thinned to several μm to several tens μm to reduce thermal expansion effects, then temperature stability is improved, but the substrate becomes more fragile and difficult to handle
Solution Approach 1:
The thin piezoelectric substrate is merged with a rigid support substrate to form a composite structure. The support substrate provides mechanical strength and handling robustness, while the thin piezoelectric layer maintains good thermal contact and reduced thermal expansion effects.
Solution Approach 2:
A composite substrate structure is created by bonding a thin piezoelectric single crystal substrate to a support substrate. This composite structure combines the advantages of both materials: the thin piezoelectric layer provides temperature stability through reduced thermal expansion, while the support substrate provides mechanical strength.
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 reduces spurious noise and enhances temperature stability in surface acoustic wave devices by optimizing the interface structure and materials, leading to improved performance and reliability.
Implementation Method 1
the first external electrode and the second external electrode are bonded to each other by ultrasonic welding
Data Source
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AI summary
Provided is a high-performance composite substrate for surface acoustic wave device which has good temperature characteristics and in which spurious caused by the reflection of a wave on a joined interface between a piezoelectric crystal film and a support substrate is reduced. The composite substrate for surface acoustic wave device includes: a piezoelectric single crystal substrate; and a support substrate, where, at a portion of a joined interface between the piezoelectric single crystal substrate and the support substrate, at least one of the piezoelectric single crystal substrate and the support substrate has an uneven structure, a ratio of an average length RSm of elements in a cross-sectional curve of the uneven structure to a wavelength λ of a surface acoustic wave when the substrate is used as a surface acoustic wave device is equal to or more than 0.2 and equal to or less than 7.0.