Longitudinally Coupled Elastic Wave Filter Wiring Layout for Miniaturization
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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 interdigital transducer electrodes with busbars and wiring lines on an inorganic insulating layer, allowing for reduced substrate area by eliminating the need for a three-dimensional crossing portion and enabling precise positioning of wiring lines to minimize electrostatic capacitance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If wiring lines are arranged to three-dimensionally cross on the piezoelectric substrate, then electrical connectivity is achieved, but the substrate surface area increases
Solution Approach 1:
The patent utilizes the vertical dimension by forming an inorganic insulating layer and positioning first wiring lines above busbars on this layer, while second wiring lines are disposed on the substrate. This three-dimensional wiring arrangement allows crossing of signal and ground lines without increasing the horizontal substrate footprint, effectively resolving the contradiction between electrical connectivity and substrate area.
Solution Approach 2:
The patent embeds the inorganic insulating layer containing first wiring lines within the overall device structure, nesting this intermediate layer between the busbars and the second wiring lines on the substrate. This nested configuration enables multiple wiring layers to coexist in a compact vertical arrangement, achieving complex electrical connections without expanding the substrate surface area.
2Length of stationary object
If a three-dimensional crossing portion is provided spaced apart from IDT electrodes, then wiring connectivity is achieved, but the device size increases
Solution Approach 1:
The patent forms the inorganic insulating layer and positions the first wiring lines above the busbars in advance, before finalizing the complete wiring arrangement. This preliminary positioning of wiring lines directly above their connection points (busbars) eliminates the need for spaced-apart three-dimensional crossing portions, thereby reducing device length while maintaining wiring connection ease through direct vertical alignment.
3Reliability
If wiring lines are positioned to minimize electrostatic capacitance variations, then signal transmission quality is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs a photolithography process that uses light blocking properties to automatically define wiring line positions. The wiring lines are formed to align with busbar patterns through self-aligned photolithography, where the busbar structure itself serves as the alignment reference. This self-service approach minimizes electrostatic capacitance variations while reducing manufacturing precision requirements, as the alignment is achieved through the patterning process rather than requiring high-precision manual positioning.
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 reduces the size of the elastic wave device, enhances electromagnetic shielding, and improves isolation characteristics by reducing the substrate area and parasitic capacitance, while maintaining effective signal transmission.
Implementation Method 1
an inorganic insulating layer covers a plurality of the first busbars or a plurality of the second busbars
Implementation Method 2
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.