SAW Filter Air-Gap Structure Using Recessed Piezoelectric Substrates
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Solution Overview
Problem
The existing methods for manufacturing surface acoustic wave devices require complex processing steps, expensive cover members with complicated shapes, and result in increased package size due to the need for forming air gaps using direct bonding without adhesives, which complicates the miniaturization of band-pass filters.
Innovation Solution
A method involving the formation of grooves and recessed portions on a piezoelectric substrate using chemical mechanical polishing (CMP) or dry etching, allowing for direct bonding of a planar cover member to create an air gap without the need for a cover member with a recessed portion, reducing size and cost while maintaining reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct bonding is used to form air gap without adhesive, then sealing property is improved, but device size is increased
Solution Approach 1:
The invention transitions from horizontal air gap formation (increasing device footprint) to vertical air gap formation through recessed portions (maintaining compact footprint). The air gap is created in the thickness direction by removing substrate portions, allowing the cover member to be bonded directly without adhesive while maintaining small device size.
2Manufacturing precision
If cover member with recessed portion is used to form air gap, then air gap formation is achieved, but manufacturing complexity and cost are increased
Solution Approach 1:
Instead of creating a recessed portion in the cover member (complex shape), the invention inverts the approach by creating recessed portions in the substrate. This allows the cover member to remain simple and planar, significantly reducing manufacturing complexity and cost while achieving the same air gap formation function.
Solution Approach 2:
The air gap structure is copied from the substrate side (recessed portions) rather than requiring complex shaping of the cover member. This simplifies the cover member design to a basic planar structure that can be easily manufactured and bonded.
3Loss of substance
If direct bonding without adhesive is used, then adhesive material cost is reduced, but processing complexity is increased
Solution Approach 1:
The substrate's own structure (recessed portions) provides the air gap function, eliminating the need for external adhesive materials. The substrate essentially creates its own bonding structure through the recessed portions, simplifying the overall manufacturing process despite the additional substrate processing 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
This approach enables the miniaturization of surface acoustic wave devices by precisely adjusting the air gap size, reducing the overall device size and cost, and enhancing reliability through direct bonding without adhesives, while eliminating the need for complex cover member shapes and processing steps.
Implementation Method 1
forming, in one principal surface of the piezoelectric substrate, grooves in portions in which an IDT electrode and a wiring electrode are to be provided, forming, on the one principal surface of the piezoelectric substrate, a metallic film at least in the grooves, forming a recessed portion by removing one portion of the piezoelectric substrate from the principal surface side of the piezoelectric substrate to form, using the metallic film located in the grooves, the IDT electrode and the wiring electrode
Implementation Method 2
bonding the cover member to the one principal surface of the piezoelectric substrate
Implementation Method 3
Direct bonding is a method in which heat is applied to the piezoelectric substrate 102 and the cover member 104 with the piezoelectric substrate 102 being in contact with the cover member 104 to make hydrogen bonds therebetween, thereby directly bonding the piezoelectric substrate 102 and the cover member 104 together. Accordingly, the surfaces of portions facing the surfaces of the piezoelectric substrate 102 and the cover member 104 which are to be bonded must include hydrophilic groups. The hydrophilic groups are to be bonded by hydrogen bonds of water molecules provided from moisture.
Data Source
AI summary
A method for manufacturing a surface acoustic wave filter device includes a step of forming grooves in one principal surface of a piezoelectric substrate, a step of embedding a metallic film in the grooves to form IDT electrodes, a step of performing a process of removing a portion of the piezoelectric substrate from the one principal surface of the piezoelectric substrate, thereby forming a recessed portion including the bottom surface in which the IDT electrodes are embedded, and a step of bonding a cover member to the piezoelectric substrate.