Composite Substrate Bonding Orientation for Thermal Strain Minimization
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Solution Overview
Problem
Conventional elastic wave devices experience low production yield due to crack generation caused by thermal stress resulting from the difference in thermal expansion coefficients and elastic moduli between piezoelectric and support substrates, especially during high-temperature processes.
Innovation Solution
A composite substrate is designed with a piezoelectric substrate and a support substrate bonded such that the in-plane maximum thermal strain is minimized, typically by rotating the substrates 0° to 360° to achieve the lowest thermal strain value or within a 10% reduction of the maximum value, using substrates like lithium tantalate and silicon, and bonding methods involving ion beam activation or organic adhesive layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bonding methods are used without optimizing thermal strain, then manufacturing is simpler, but cracks occur during high-temperature processes reducing production yield
Solution Approach 1:
The patent applies parameter changes by optimizing the bonding orientation angle to control thermal strain. Specifically, it determines the maximum and minimum thermal strain amounts when substrates are bonded at different angles (0° to 360° rotation), and selects a bonding angle where the in-plane maximum thermal strain is minimized or reduced by 10% or more from the maximum value. This parameter optimization prevents crack generation during high-temperature reflow processes while maintaining manufacturing feasibility.
Solution Approach 2:
The patent implements preliminary action by calculating and determining the optimal bonding orientation before the actual bonding process. The method involves computing thermal strain amounts at various angles, identifying the minimum strain configuration, and then bonding the piezoelectric substrate to the support substrate at this predetermined optimal angle. This preliminary optimization prevents cracks before they can occur during subsequent high-temperature manufacturing steps.
2Temperature
If substrates are bonded without considering thermal strain optimization, then the bonding process is faster, but thermal stress causes cracks reducing heat resistance
Solution Approach 1:
The patent changes the bonding parameter from arbitrary orientation to optimized orientation based on thermal strain calculations. By determining the bonding angle that minimizes in-plane maximum thermal strain (or reduces it by 10% or more from the maximum), the patent enables the composite substrate to withstand high-temperature processes without crack generation, thereby improving heat resistance while controlling the complexity through systematic parameter optimization.
3Ease of manufacture
If high-temperature processes are performed on composite substrates with large thermal expansion differences, then manufacturing flexibility is improved, but thermal stress generates cracks
Solution Approach 1:
The patent addresses thermal stress by changing the bonding orientation parameter to minimize in-plane maximum thermal strain. By selecting a bonding angle where thermal strain is reduced by 10% or more from the maximum value, the patent enables high-temperature manufacturing processes to be performed without crack generation, thus maintaining process flexibility while eliminating the harmful thermal stress effect.
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 suppresses crack generation during high-temperature treatments, enhancing the heat resistance and manufacturing ease of the composite substrate for elastic wave devices.
Implementation Method 1
a piezoelectric substrate which has an anisotropy and is capable of transmitting an elastic wave
Implementation Method 2
a support substrate which has an anisotropy and a smaller thermal expansion coefficient than that of the piezoelectric substrate
Implementation Method 3
a piezoelectric substrate and/or a support substrate having an anisotropic thermal expansion coefficient and an anisotropic elastic modulus (Young's modulus)
Data Source
AI summary
A composite substrate is provided, including a piezoelectric substrate which is capable of transmitting an elastic wave, and a support substrate, which has a smaller thermal expansion coefficient than that of the piezoelectric substrate, bonded to each other. The in-plane maximum thermal strain amount, which is the largest thermal strain amount in the plane of the composite substrate, has a minimum value and a maximum value when the piezoelectric substrate and the support substrate are relatively rotated 0° to 360°, and the piezoelectric substrate and the support substrate are bonded to each other so that the in-plane maximum thermal strain amount has the minimum value or a value in the vicinity thereof.