SAW Cover Strip Reinforcement for Thermal Warping Control
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Solution Overview
Problem
Existing acoustic wave devices face challenges in suppressing warping of the cover and thermal expansion, which affect the electrical characteristics and reliability of the device, particularly due to the mismatch in thermal expansion coefficients between the piezoelectric substrate and the cover.
Innovation Solution
The acoustic wave device incorporates a support substrate with a smaller thermal expansion coefficient than the piezoelectric substrate, along with a reinforcing layer of strip conductors on the cover that overlap the space above the excitation electrode, to reduce thermal expansion and warping, while improving heat dissipation and mechanical reinforcement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cover is provided to seal the excitation electrode, then the electrode is protected and acoustic wave propagation is facilitated, but the cover warps toward the space side due to thermal expansion mismatch
Solution Approach 1:
The reinforcing layer is segmented into a stripe pattern with multiple parallel strips rather than a continuous solid layer. This segmentation reduces the overall area of the reinforcing layer that contacts the piezoelectric substrate, thereby reducing the total thermal expansion force while maintaining localized reinforcement at critical positions to prevent cover warping.
Solution Approach 2:
The reinforcing layer is positioned specifically on the space side of the cover, targeting the region where warping occurs. The stripe pattern provides localized reinforcement at critical positions along the cover, applying strength where needed while minimizing unnecessary material and thermal expansion influence on the piezoelectric substrate.
2Shape
If a solid reinforcing layer is provided on the cover, then warping is suppressed, but thermal expansion of the piezoelectric substrate increases due to the conductor material
Solution Approach 1:
The reinforcing layer is divided into multiple parallel stripes with gaps between them. This segmentation reduces the total area of conductor material in contact with the piezoelectric substrate, thereby reducing the cumulative thermal expansion effect while maintaining sufficient reinforcement to suppress cover warping through the distributed stripe structure.
Solution Approach 2:
The reinforcing layer is positioned specifically on the space side of the cover rather than covering the entire surface. This localized placement provides reinforcement where warping occurs while minimizing the total conductor area that contributes to thermal expansion of the piezoelectric substrate.
3Ease of manufacture
If the thermal expansion coefficient mismatch between piezoelectric substrate and cover is large, then device assembly is easier, but electrical characteristics deteriorate due to thermal stress
Solution Approach 1:
The stripe pattern parameters (width, spacing, length) are optimized to achieve the right balance. The stripes are spaced and sized to provide sufficient reinforcement for warping suppression while maintaining gaps that allow thermal expansion accommodation, thereby reducing thermal stress on the piezoelectric substrate and preserving electrical characteristics.
4Stability of the object's composition
If a reinforcing layer is added to suppress warping, then cover stability improves, but device complexity increases
Solution Approach 1:
The reinforcing layer is implemented as a simple stripe pattern that can be easily fabricated using standard photolithography and metal deposition processes. The segmented stripe design is simpler to manufacture than a solid continuous layer while providing equivalent or superior warping suppression through distributed reinforcement.
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 suppresses the thermal expansion of the piezoelectric substrate, maintains the temperature compensation effect, and enhances the reliability and stability of the acoustic wave device by reducing the probability of warping and improving shearing stress resistance.
Implementation Method 1
a support substrate which is located on a lower surface of the piezoelectric substrate and has a smaller thermal expansion coefficient than that of the piezoelectric substrate
Implementation Method 2
an excitation electrode positioned on an upper surface of the piezoelectric substrate
Implementation Method 3
The acoustic wave is for example a surface acoustic wave (SAW)
Data Source
AI summary
A SAW device includes a piezoelectric substrate, a support substrate which is located on a lower surface of the piezoelectric substrate and has a smaller thermal expansion coefficient than that of the piezoelectric substrate, an IDT electrode located on the piezoelectric substrate, a cover forming a space above the IDT electrode, and a plurality of first strip conductors which extend alongside each other on the cover and at least a part of which overlaps the space when viewed on a plane.