SAW Electrode Structure to Prevent IDT Hillocks During Resin Curing
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Solution Overview
Problem
Surface acoustic wave devices with three-dimensionally intersecting wiring patterns on piezoelectric substrates face challenges in achieving size reduction while maintaining high power durability, as the use of Al—Cu alloy films with a twin crystal structure can lead to the formation of hillocks or protrusions on IDT electrodes during heat curing of insulating films.
Innovation Solution
The use of Al films or Al—Cu alloy films with a Cu content not exceeding the solubility limit at 25°C, combined with thermosetting resin insulating layers, specifically polyimide, which are heat-cured at temperatures between 305°C to 350°C, prevents the formation of hillocks and enhances power durability by ensuring stable electrode structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Al-Cu alloy films with high Cu content are used to improve power durability, then power durability is improved, but hillocks or protrusions are formed on IDT electrodes during heat curing
Solution Approach 1:
The patent changes the chemical composition parameters of the Al-Cu alloy film by precisely controlling the Cu content to be 0.01 wt% or more but below the solubility limit at the heat curing temperature. This parameter optimization allows the film to maintain excellent power durability while preventing Cu precipitation that causes hillock formation during heat curing processes.
Solution Approach 2:
The patent applies different Cu concentration levels in different regions of the alloy film structure, maintaining higher Cu content near the interface with the piezoelectric substrate to maximize power durability, while keeping the overall Cu content below the solubility limit to prevent hillock formation on the electrode surface during heat curing.
2Volume of moving object
If three-dimensionally intersecting wiring patterns are used for size reduction, then device size is reduced, but the complexity of manufacturing and assembly increases
Solution Approach 1:
The patent transitions from planar two-dimensional wiring layouts to three-dimensional intersecting wiring patterns that extend in multiple spatial dimensions. This allows signal paths to intersect without electrical interference by separating them in the vertical dimension, achieving compact device size while maintaining manufacturing feasibility through standardized multi-layer fabrication processes.
Solution Approach 2:
The patent implements nested wiring structures where multiple wiring layers are stacked vertically with insulating films between them, creating a compact three-dimensional configuration. The IDT electrodes and interconnection wires are arranged in nested layers, allowing dense integration while using conventional multi-layer fabrication techniques to manage manufacturing complexity.
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 allows for size reduction of surface acoustic wave devices with improved power durability and prevents the formation of hillocks on IDT electrodes, ensuring stable and efficient operation.
Implementation Method 1
thermosetting resin insulating layers, specifically polyimide, which are heat-cured at temperatures between 305°C to 350°C
Implementation Method 2
surface acoustic wave devices used as, for example, band-pass filters or resonators
Implementation Method 3
a plurality of wiring patterns having different potentials that are arranged on a piezoelectric substrate
Data Source
AI summary
A surface acoustic wave device includes first interconnections and second interconnections connected to a potential different from a potential connected to the first interconnections that are arranged on a piezoelectric substrate. The first interconnections three-dimensionally intersect with the second interconnections with insulating layers made of a thermosetting resin, disposed therebetween. Interdigital electrodes defining IDTs are films which have six-fold rotational symmetric spots appearing in an XRD pole figure and which are defined by Al films or Al—Cu alloy films containing Cu in an amount not greater than the solubility limit at about 25° C.