Surface Acoustic Wave Device Three-Dimensional Wiring Rupture Prevention
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Solution Overview
Problem
Surface acoustic wave devices with three-dimensional wiring portions are prone to ruptures due to stress caused by differences in the coefficients of linear expansion between the surrounding wall and the insulating layer, leading to reliability issues.
Innovation Solution
A surface acoustic wave device design that includes a supporting member with openings to enclose three-dimensional wiring portions, an insulating layer between intersecting wiring lines, and an adhesiveness improving film to enhance substrate adhesion, preventing stress-induced ruptures by isolating wiring lines from expansion differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surrounding wall and insulating layer are used to enclose and insulate three-dimensional wiring portions, then electrical insulation and device compactness are improved, but stress-induced ruptures occur due to differential thermal expansion
Solution Approach 1:
A buffer layer is introduced between the insulating layer and the surrounding wall to act as a stress-absorbing intermediary. This buffer layer has a coefficient of linear expansion between those of the insulating layer and surrounding wall, effectively mediating the differential thermal expansion stresses and preventing wiring line ruptures while maintaining electrical insulation.
Solution Approach 2:
The coefficient of linear expansion of the buffer layer is specifically selected to be between those of the insulating layer and surrounding wall. By changing this physical parameter, the buffer layer creates a gradient that progressively absorbs thermal expansion stresses, preventing sudden stress concentration that would cause wiring line ruptures.
2Volume of moving object
If the size and thickness of the device are reduced by using a compact structure, then device miniaturization is achieved, but wiring lines become more susceptible to stress and ruptures
Solution Approach 1:
The three-dimensional wiring portion is nested within the hollow space enclosed by the supporting member, insulating layer, and surrounding wall. This nested structure allows the wiring lines to be protected within the compact device volume while the buffer layer provides stress relief, achieving both miniaturization and reliability.
3Object-affected harmful factors
If different materials are used for the insulating layer and surrounding wall to reduce parasitic capacitance, then electrical characteristics are improved, but differential thermal expansion stress increases
Solution Approach 1:
The coefficient of linear expansion of the buffer layer is specifically selected to be between those of the insulating layer and surrounding wall. By changing this physical parameter, the buffer layer creates a gradient that progressively absorbs thermal expansion stresses, preventing sudden stress concentration that would cause wiring line ruptures.
Solution Approach 2:
The patent uses a composite structure consisting of the insulating layer, buffer layer, and surrounding wall made of different materials. This composite structure allows each layer to have optimized properties: the insulating layer for electrical insulation, the buffer layer for stress management, and the surrounding wall for structural support, while collectively reducing parasitic capacitance.
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 design effectively prevents ruptures at three-dimensional wiring portions, increasing the reliability and reducing the size of the device while maintaining low-temperature curing processes and simplifying manufacturing.
Implementation Method 1
a piezoelectric substrate 102 composed of, for example, LiTaO3. An IDT electrode 103 is formed on the piezoelectric substrate 102. Surface acoustic waves are excited by applying an AC voltage to the IDT electrode 103.
Implementation Method 2
an adhesiveness improving film having an adhesiveness to the piezoelectric substrate that is higher than an adhesiveness of the supporting member to the piezoelectric substrate and located on the first main surface of the piezoelectric substrate.
Data Source
AI summary
A highly reliable surface acoustic wave device includes wiring lines that do not easily rupture at a three-dimensional wiring portion. The surface acoustic wave device includes a plurality of surface acoustic wave elements located on a piezoelectric substrate, a supporting member arranged on the piezoelectric substrate so as to enclose vibrating portions including electrodes such as IDT electrodes, and a cover member stacked so as to cover openings of the supporting member and to define hollow spaces facing vibrating electrodes. Furthermore, a three-dimensional wiring portion at which a first wiring line and a second wiring line are stacked with an insulating layer interposed therebetween is provided on the piezoelectric substrate. The three-dimensional wiring portion is enclosed by the supporting member, and thereby disposed inside a space enclosed by the piezoelectric substrate, the supporting member, and the cover member.