Gradient Composite Substrate for Low-Stress Elastic Wave Devices
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Solution Overview
Problem
The formation of composite substrates for elastic wave devices is complicated, and existing solutions face issues with thermal stress and peeling due to differences in thermal expansion between piezoelectric and support substrates, leading to degraded frequency characteristics and substrate deformation.
Innovation Solution
A composite substrate is formed by bonding a piezoelectric substrate with a support substrate having a lower coefficient of thermal expansion, where the support substrate's thermal expansion coefficient or Young's modulus is gradually decreased from one surface to an intermediate position, creating a functionally gradient material to reduce thermal stress and peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a composite substrate is formed by bonding a piezoelectric substrate onto a support substrate having a low coefficient of thermal expansion, then frequency-temperature characteristics are improved, but thermal stress causes substrate deformation and peeling
Solution Approach 1:
The patent applies parameter changes by creating a functionally gradient support substrate where the coefficient of thermal expansion varies continuously from the first surface (in contact with piezoelectric substrate) to the second surface. This gradual parameter change reduces thermal stress and prevents peeling while maintaining improved frequency-temperature characteristics.
Solution Approach 2:
The patent uses composite materials by forming a support substrate with a functionally gradient structure consisting of multiple layers or regions with different coefficients of thermal expansion. This composite structure allows the substrate to bridge the thermal expansion mismatch between the piezoelectric substrate and the external environment, reducing stress and preventing delamination.
2Ease of manufacture
If heat is applied to the composite substrate in the process for forming elastic wave devices, then electrodes are formed, but substrate deformation degrades electrode width accuracy
Solution Approach 1:
The functionally gradient support substrate changes the thermal expansion parameter gradually through its thickness, which reduces warpage and deformation during heating processes. This maintains electrode width accuracy while still allowing the photolithographic electrode formation process to be performed.
3Strength
If a composite substrate having a three-layer structure with a compensating layer is used, then thermal stress is reduced, but the process becomes very complicated
Solution Approach 1:
The patent applies local quality by creating a support substrate with spatially varying properties - the coefficient of thermal expansion changes locally from one surface to the other. This single substrate with localized property variations replaces the need for multiple separate layers, reducing structural complexity while maintaining thermal stress resistance.
Solution Approach 2:
The patent merges the functions of multiple separate layers (piezoelectric substrate, compensating layer, support substrate) into an integrated composite structure where the support substrate itself has the gradient functionality. This consolidation reduces the number of discrete components and simplifies the overall 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 approach simplifies the substrate structure, reduces warpage and thermal stress, and improves frequency stability by matching the temperature coefficient of frequency, while preventing peeling between substrates, resulting in enhanced performance of elastic wave devices.
Implementation Method 1
the support substrate has a first surface bonded to the piezoelectric substrate and an unbonded second surface opposite to the first surface, and one specific characteristic value selected from the coefficient of thermal expansion and the Young's modulus is decreased along a thickness direction from the second surface to an intermediate position between the first surface and the second surface
Data Source
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AI summary
A composite substrate 10 is a substrate formed by bonding a piezoelectric substrate 12 and a support substrate 14 having a coefficient of thermal expansion lower than that of the piezoelectric substrate 12. The support substrate 14 has a first surface 14a bonded to the piezoelectric substrate 12 and a second surface 14b opposite to the first surface 14a. The coefficient of thermal expansion of the support substrate 14 is decreased along a thickness direction from the second surface 14b to an intermediate position 14c located between the first surface 14a and the second surface 14b.