Longitudinally Coupled Resonator Wiring for Smaller Elastic Wave Filters
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Solution Overview
Problem
Elastic wave devices with longitudinally coupled resonator filters on piezoelectric substrates face challenges in reducing the size due to the need for three-dimensional crossing of wiring lines, which increases the substrate surface area and complicates miniaturization.
Innovation Solution
The design incorporates an inorganic insulating layer to cover busbars and position wiring lines in a way that reduces the substrate area by eliminating the need for a three-dimensional crossing portion, allowing for a more compact configuration with busbars connected to the same potential and wiring lines extending in the elastic wave propagation direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wiring lines are arranged to three-dimensionally cross in a portion spaced apart from IDT electrodes, then electrical connection is achieved, but the piezoelectric substrate surface area increases
Solution Approach 1:
The patent utilizes the thickness direction (z-direction) of the piezoelectric substrate to arrange wiring lines at different heights. Specifically, first wiring lines are placed on the piezoelectric substrate surface while second wiring lines are positioned on an insulating film layer above it, enabling three-dimensional crossing without increasing the planar footprint. This vertical layering approach resolves the contradiction by achieving electrical connectivity while maintaining compact substrate area.
Solution Approach 2:
The patent implements a nested structure where multiple wiring lines are embedded within different layers of the substrate assembly. The first wiring lines are integrated into the substrate, while second wiring lines are nested within an insulating film layer that covers the substrate. This nested arrangement allows wiring lines to cross each other in the thickness direction without requiring additional lateral space, thus reducing the overall substrate surface area while maintaining functional electrical connections.
2Ease of operation
If three-dimensional crossing portion is provided away from IDT electrodes, then wiring connection is enabled, but device size increases
Solution Approach 1:
The patent resolves the volume increase issue by transitioning from planar wiring arrangement to three-dimensional layering. First wiring lines extend in the elastic wave propagation direction on the substrate surface, while second wiring lines cross them vertically through the insulating film layer. This dimensional transition allows wiring connections to be made within the existing device footprint without requiring additional lateral or vertical space, thus maintaining compact device volume while enabling necessary electrical connections.
Solution Approach 2:
The patent merges the wiring line crossing function with the existing layered structure of the elastic wave device. The insulating film layer, originally intended for electrical isolation, is simultaneously utilized as a carrier for the second wiring lines. This merging of functions allows the wiring connections to be integrated into the existing device architecture without requiring separate crossing structures or additional space, thereby preventing device volume increase while enabling necessary wiring connections.
3Reliability
If wiring lines cross with insulating film interposed, then electrical isolation is achieved, but substrate area increases
Solution Approach 1:
The insulating film layer serves multiple functions simultaneously: it provides electrical isolation between the first wiring lines on the substrate and the second wiring lines above, while also acting as a structural carrier for the second wiring lines. This multi-functionality allows the insulating film to enable wiring crossings without requiring additional lateral space, thus achieving reliable electrical isolation while maintaining compact substrate area.
Solution Approach 2:
The patent achieves electrical isolation by utilizing the thickness direction rather than expanding laterally. The insulating film layer is positioned in the z-direction between the first and second wiring lines, providing electrical isolation without requiring the wiring lines to be spaced apart in the planar directions. This vertical isolation approach maintains compact substrate area while ensuring reliable electrical separation between different wiring layers.
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 configuration effectively reduces the size of the elastic wave device, minimizes electrostatic capacitance variations, and provides electromagnetic shielding, leading to improved performance and reduced substrate area usage.
Implementation Method 1
An inorganic insulating layer covers a plurality of the first busbars or a plurality of the second busbars on at least one of the first end side and the second end side
Implementation Method 2
a second wiring line that is disposed on the piezoelectric substrate so as to three-dimensionally crosses the first wiring line with the inorganic insulating layer interposed between the first wiring line and the second wiring line
Implementation Method 3
a piezoelectric substrate and a first longitudinally coupled resonator elastic wave filter that is disposed on the piezoelectric substrate
Data Source
AI summary
A longitudinally coupled resonator elastic wave filter is disposed on a piezoelectric substrate. IDT electrodes include first and second busbars. An inorganic insulating layer is provided on at least one side in a direction perpendicular or substantially perpendicular to an elastic wave propagation direction to cover the first or second busbars, and a first wiring line is disposed on the inorganic insulating layer to extend in the elastic wave propagation direction. A second wiring line three-dimensionally crosses the first wiring line with the inorganic insulating layer interposed therebetween. The first wiring line is connected to busbars, which are connected to the same potential, by extending through the inorganic insulating layer.