SAW Filter Laser Undersurface Structuring for Spurious Suppression
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Solution Overview
Problem
Existing SAW filter manufacturing methods using undersurface grinding or etching to form uneven structures on crystal substrates fail to effectively control elastic wave reflection, leading to spurious components and increased labor and cost due to the need for masking and rough surface formation.
Innovation Solution
A SAW filter manufacturing method involving the use of a laser beam to create projections and depressions on the undersurface of a piezoelectric substrate, with a distance of 1 μm or more from the vertex of projecting portions to the bottom surface of recessed portions, allowing precise control of elastic wave reflection without forming structures in predetermined regions like the outer peripheral edge, thereby reducing labor and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If undersurface grinding is used to form uneven structure on crystal substrate, then elastic wave scattering is improved, but manufacturing precision and control of elastic wave reflection deteriorate
Solution Approach 1:
The patent replaces the mechanical undersurface grinding process with laser beam processing. The laser beam forms a structure with projections and depressions on the undersurface of the piezoelectric substrate by irradiation, eliminating the need for mechanical contact and providing precise control over the uneven structure geometry, thereby achieving both effective elastic wave scattering and precise manufacturing control
Solution Approach 2:
The patent changes the method of forming the uneven structure from mechanical grinding to laser processing, which allows precise control of parameters such as projection height, depression depth, and pattern geometry. The distance from vertex of projecting portion to bottom surface of recessed portion is controlled at 1 μm or more, enabling precise manipulation of elastic wave reflection characteristics
2Reliability
If rough surface is formed on margin area by etching or blasting, then elastic wave reflection control is improved, but manufacturing cost and complexity increase due to mask formation
Solution Approach 1:
The patent replaces chemical etching or blasting processes with laser beam processing. The laser directly forms the uneven structure on the undersurface without requiring mask formation, thereby eliminating the additional manufacturing steps and reducing overall process complexity while maintaining precise control over the margin area structure
Solution Approach 2:
The patent extracts the mask formation step from the manufacturing process by using laser processing that can directly write the desired pattern without masks. The laser beam can be selectively applied to margin areas or excluded from predetermined regions including outer peripheral edge portions, achieving the same effect without the intermediary masking step
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 enables the precise control of elastic wave reflection, suppressing spurious components and reducing manufacturing costs by forming structures with high accuracy using laser processing, resulting in improved SAW filter quality and transverse rupture strength.
Implementation Method 1
forming a structure having projections and depressions on an undersurface side of the piezoelectric substrate by irradiating the piezoelectric substrate with a laser beam of a wavelength absorbable by the piezoelectric substrate from the undersurface side
Implementation Method 2
A SAW filter using a surface acoustic wave propagating on a piezoelectric substrate
Data Source
AI summary
There is provided a SAW filter manufacturing method for manufacturing a SAW filter from a piezoelectric substrate having planned dividing lines set on a top surface of the piezoelectric substrate, and having a device including comb-shaped electrodes in regions demarcated by the planned dividing lines. The method includes a structure forming step of forming a structure having projections and depressions on an undersurface side of the piezoelectric substrate by irradiating the piezoelectric substrate with a laser beam of a wavelength absorbable by the piezoelectric substrate from the undersurface side of the piezoelectric substrate, and a dividing step of dividing the piezoelectric substrate along the planned dividing lines after the structure forming step.