Composite Substrate with Partially Planarized Bonding Surface
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Solution Overview
Problem
Existing composite substrates for surface acoustic wave devices face challenges with heat resistance and signal degradation due to indirect bonding and insufficient contact area between piezoelectric and supporting substrates, which are exacerbated by the reflection of bulk waves.
Innovation Solution
A composite substrate with partially planarized bonding surfaces featuring protrusions and flat portions, where the arithmetic average roughness of flat portions is 1 nm or less and the roughness of other portions is 10 nm or more, allowing for direct bonding and effective scattering of bulk waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thin film is formed on a substrate by a sputtering method, then the film can be formed at a low temperature, but the film has a large number of pinholes and poor film quality
Solution Approach 1:
The patent uses a composite structure consisting of a porous base layer and a non-porous thin film layer. The porous layer serves as a buffer that accommodates thermal stress and prevents pinhole formation, while the non-porous layer provides the required film quality. This composite material approach allows low-temperature formation without compromising film integrity.
Solution Approach 2:
The patent applies different structural qualities to different layers: the base layer is designed with porous structure to handle mechanical stress and allow thermal expansion, while the thin film layer is made non-porous to provide high-quality functional properties. This local differentiation of material properties resolves the contradiction between low-temperature formation and film quality.
2Temperature
If a thin film is formed on a substrate by an evaporation method, then the film can be formed at a low temperature, but the adhesion between the film and the substrate is poor
Solution Approach 1:
The patent employs a composite structure with a porous base layer and a non-porous thin film layer. The porous base layer provides mechanical interlocking and stress relief, while the non-porous thin film layer ensures strong adhesion to the substrate. This composite approach enables low-temperature formation while maintaining excellent adhesion strength.
Solution Approach 2:
The patent differentiates the structural quality between layers: the base layer has porous structure for mechanical anchoring and stress accommodation, while the thin film layer has dense non-porous structure for strong adhesion and functional performance. This local quality differentiation resolves the adhesion contradiction.
3Adaptability or versatility
If the number of elements is increased in order to improve the functionality of a sensor, then the sensor can detect multiple components, but the sensor becomes large in size
Solution Approach 1:
The patent creates a multi-functional sensor array where each sensing element can detect different chemical components. By arranging multiple sensing elements with different selectivities on a single substrate, the sensor system achieves the ability to detect multiple components simultaneously without requiring separate sensor devices, thus maintaining compact size while improving versatility.
Solution Approach 2:
The patent divides the sensing function into multiple discrete sensing elements arranged in an array on a single substrate. Each element is responsible for detecting specific components, and the collective array provides comprehensive multi-component detection capability. This segmentation allows high functionality to be achieved within a compact integrated 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 solution enhances heat resistance and improves signal quality by securing a sufficient contact area and scattering bulk waves, thereby improving the characteristics of surface acoustic wave devices.
Implementation Method 1
In order to reduce stress on a thin film, a composite substrate in the form of a thin film on a porous layer is used
Implementation Method 2
When a thin film is formed on a substrate by a sputtering method or an evaporation method
Implementation Method 3
it has come to light by experimentation that a composite substrate in the form of a thin film on a porous layer can form high-quality thin films without pinholes
Implementation Method 4
the adhesion between the film and the substrate is poor
Data Source
Figure 1~2
Figure 3(a1)~3(d)
Figure 4~5
AI summary
In a composite substrate 10, a bonding surface 21 of a piezoelectric substrate 20 is an irregular surface which is partially planarized. The irregular surface which is partially planarized includes a plurality of protrusions 23, each having a flat portion 25 on the tip thereof. The piezoelectric substrate 20 and the supporting substrate 30 are directly bonded to each other at the flat portions 25. By forming the bonding surface 21 into an irregular surface (rough surface) and providing flat portions 25 at the same time, it is possible to secure a sufficient contact area between the piezoelectric substrate 20 and the supporting substrate 30. Accordingly, in the composite substrate in which the piezoelectric substrate 20 and the supporting substrate 30 are bonded to each other, the bonding surface 21 can be roughened and direct bonding can be performed. Furthermore, it is possible to obtain a surface acoustic wave device in which heat resistance is enhanced by performing direct bonding without using an adhesive, and also bulk waves are scattered because of the roughened bonding surface, thus improving characteristics.