Composite Piezoelectric Substrate With Split Roughness Bonding
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Solution Overview
Problem
The challenge is to enhance the bonding strength between a piezoelectric substrate and a sapphire substrate while minimizing the reflection of bulk waves at the bonding interface, as increasing surface roughness to reduce wave reflection leads to decreased bonding strength in existing composite substrates for piezoelectric devices.
Innovation Solution
A composite substrate is created with a sapphire substrate having a specific arithmetic mean roughness of 0.1 μm to 0.5 μm on one surface and an alumina layer with a roughness of 0.1 μm or less on the opposing surface, directly bonded to the piezoelectric substrate, using a process that includes roughening and alumina layer formation to achieve optimal bonding without adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the surface roughness of the support substrate is increased to reduce the reflection of bulk waves, then the reflection of bulk waves is reduced, but the bonding strength between the support substrate and the piezoelectric substrate is reduced
Solution Approach 1:
The invention applies different surface roughness values to different surfaces of the same substrate. The support substrate has a first surface with Ra of 0.1-0.5 μm (for wave reflection reduction) and a second surface with Ra of 0.01-0.1 μm (for bonding strength). This local differentiation allows each surface to optimize for its specific function without compromising the other.
Solution Approach 2:
The invention segments the surface roughness property into two distinct zones on the support substrate: the first surface (element formation surface) with higher roughness for acoustic wave management, and the second surface (bonding surface) with lower roughness for mechanical bonding. This segmentation resolves the contradiction by allowing independent optimization of each function.
2Object-generated harmful factors
If a roughening process is applied to the support substrate to reduce bulk wave reflection, then bulk wave reflection is reduced, but the bonding strength is reduced
Solution Approach 1:
The roughening process is applied selectively to only the first surface (element formation surface) of the support substrate with Ra of 0.1-0.5 μm, while the second surface (bonding surface) is maintained with Ra of 0.01-0.1 μm through separate processing. This localized application of roughening achieves wave reflection reduction without compromising bonding strength.
Solution Approach 2:
The processing steps are segmented into separate operations: roughening the first surface for acoustic performance, then separately preparing the second surface for bonding with appropriate roughness. This process segmentation allows independent optimization of each surface's properties.
Data Source
AI summary
A composite substrate of the present disclosure includes a piezoelectric substrate having a first surface which is an element formation surface and a second surface which is a back surface of the first surface, a sapphire substrate having a third surface which is disposed opposing a second surface and a fourth surface which is a back surface of the third surface, a fifth surface opposing the second surface, and a sixth surface opposing the third surface. It includes an alumina layer bonding the second surface and the third surface, and an arithmetic mean roughness Ra of the third surface is 0.1 μm or more and 0.5 μm or less. The arithmetic mean roughness Ra of the fifth surface is 0.1 μm or less and is smaller than the arithmetic mean roughness Ra of the third surface.