Composite Substrate Bonding with Filled Asperities for Bubble Control
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Solution Overview
Problem
The existing surface acoustic wave devices face issues with bubble formation when bonding piezoelectric and support substrates due to minute asperities on the piezoelectric substrate, leading to air entrapment and reduced adhesion force between the substrates.
Innovation Solution
A composite substrate manufacturing method involving the formation of minute asperities on the piezoelectric substrate, followed by applying a filler to fill these asperities and mirror-polishing the surface to reduce roughness, allowing for bonding with an adhesive layer that minimizes bubble formation and enhances adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If minute asperities are formed on the piezoelectric substrate to suppress spurious waves, then the occurrence of spurious is suppressed, but air may be entrapped during bonding causing bubbles to generate inside the composite substrate
Solution Approach 1:
The invention divides the bonding interface into two functional zones: the piezoelectric substrate surface with asperities for spurious suppression, and a separate flat adhesive application surface created by filling and polishing, allowing both functions to coexist without interference
Solution Approach 2:
The invention introduces an adhesive layer as an intermediary between the asperity surface and the support substrate, applying it to a filled and polished surface that eliminates air entrapment while preserving the underlying asperities' spurious suppression function
2Strength
If adhesive is applied to the asperity surface to bond substrates, then bonding is achieved, but air may enter between adhesive surfaces causing bubbles inside the adhesive layer
Solution Approach 1:
The invention performs filling and polishing of the adhesive application surface before adhesive application, pre-eliminating air entrapment pathways and creating a bubble-free bonding interface while maintaining the asperities' functional properties
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 method effectively prevents bubble formation within the composite substrate, increasing the adhesion force between the piezoelectric and support substrates while maintaining the thermal expansion coefficient benefits, thus improving the device's performance and reliability.
Implementation Method 1
applying a filler to the one surface to fill the minute asperities, thereby forming a filling layer
Implementation Method 2
mirror-polishing a surface of the filling layer to such an extent that an arithmetic mean roughness Ra of the surface of the filling layer is smaller than an arithmetic mean roughness Ra of the one surface in the step (a)
Implementation Method 3
bonding the surface of the filling layer and a surface of the support substrate to each other with an adhesive layer interposed therebetween
Implementation Method 4
bonding, to the piezoelectric substrate, the support substrate having a smaller thermal expansion coefficient than the piezoelectric substrate, changes in dimensions of the piezoelectric substrate depending on temperature changes are suppressed
Implementation Method 5
bulk waves are generated as one type of acoustic waves along with the surface acoustic waves near the comb-shaped electrodes and then reach the rear surface of the piezoelectric substrate. However, the bulk waves are scattered by the asperities formed in the rear surface
Data Source
AI summary
According to a composite substrate manufacturing method of the present invention, (a) a piezoelectric substrate having minute asperities formed in a rear surface thereof, and a support substrate having a smaller thermal expansion coefficient than the piezoelectric substrate are prepared, (b) a filler is applied to the rear surface 11a to fill the minute asperities, thereby forming a filling layer, (c) a surface of the filling layer is mirror-polished to such an extent that an arithmetic mean roughness Ra of the surface of the filling layer is smaller than an arithmetic mean roughness Ra of the rear surface 11a in a state of above (a), and (d) the surface of the filling layer and a surface of the support substrate are bonded to each other with an adhesive layer interposed therebetween, thereby forming a composite substrate.