SAW Substrate Backside Roughness for Lower Spurious Reflections
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Solution Overview
Problem
Surface acoustic wave devices face challenges in reducing spurious reflections from the substrate's second surface, leading to unwanted frequency components and defects due to residual stress from roughening processes.
Innovation Solution
A substrate with specific surface roughness parameters, including arithmetic mean roughness (Ra) of 0.2 μm to 0.4 μm and maximum height (Rmax) of 2.5 μm to 4.5 μm, is used, which scatters bulk waves and reduces reflected waves, while maintaining small mean spacing of local peaks and irregularities to minimize defects and residual stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the second surface is roughened to reduce spurious reflections, then reflected waves are reduced, but defects and residual stress increase
Solution Approach 1:
The patent applies parameter changes by precisely controlling the arithmetic mean roughness (Ra) within 0.05-0.5 μm and the correlation length (lc) within 1-10 μm. This optimized parameter range allows the surface to scatter bulk waves effectively while minimizing the generation of defects and residual stress during the roughening process
Solution Approach 2:
The patent applies partial action by implementing moderate surface roughening rather than extreme roughness. The controlled Ra range of 0.05-0.5 μm provides sufficient scattering to reduce spurious reflections while avoiding excessive roughness that would cause significant defects and residual stress
2Object-generated harmful factors
If the arithmetic mean roughness (Ra) is increased to scatter bulk waves, then spurious reflections are reduced, but the mean spacing of irregularities increases causing more defects
Solution Approach 1:
The patent resolves this contradiction by simultaneously optimizing two parameters: Ra (arithmetic mean roughness) and lc (correlation length). By controlling Ra within 0.05-0.5 μm and lc within 1-10 μm, the surface provides adequate scattering while maintaining small mean spacing of irregularities, preventing excessive defects
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 substrate effectively reduces spurious reflections and defects, enhancing the performance of surface acoustic wave filters by scattering bulk waves and minimizing warpage and cracks caused by residual stress.
Implementation Method 1
the second surface has an arithmetic mean roughness (Ra) of 0.2 μm to 0.4 μm... the substrate effectively reduces spurious reflections and defects, enhancing the performance of surface acoustic wave filters by scattering bulk waves
Implementation Method 2
A surface acoustic wave device is a device that converts an electrical signal into a surface acoustic wave... constituted of a piezoelectric material
Data Source
AI summary
A substrate for a surface acoustic wave device is constituted of a piezoelectric material and includes a first surface on which a surface acoustic wave propagates, and a second surface located opposite to the first surface. The second surface has an arithmetic mean roughness (Ra) of 0.2 μm to 0.4 μm, and there is satisfied either of the relationship between the arithmetic mean roughness (Ra) and mean spacing (S) of local peaks of Ra/S≥11, and the relationship between the arithmetic mean roughness (Ra) and mean spacing (Sm) of irregularities of Ra/Sm≥6.7. Further, the second surface has a maximum height (Rmax) of 2.5 μm to 4.5 μm, and there is satisfied either of the relationship between the maximum height (Rmax) and mean spacing (S) of local peaks of Rmax/S≥130, and the relationship between the maximum height (Rmax) and mean spacing (Sm) of irregularities of Rmax/Sm≥80.