Layered Electrode Migration Prevention in Acoustic Wave Devices
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Solution Overview
Problem
Acoustic wave devices suffer from migration issues in electrode films, leading to potential breaks and short circuits in wiring electrodes, particularly in aluminum or gold films, due to vibrations and heat from high-frequency power.
Innovation Solution
The use of a layered metal film for the second electrode film, with the lowermost layer made of alloys like aluminum-copper, nickel-chromium, or titanium, and extending to the side surfaces, effectively inhibits migration by reducing resistance and preventing whisker formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer aluminum or gold electrode film is used for wiring electrodes, then the manufacturing process is simple and cost-effective, but migration occurs under acoustic wave vibrations and heat, causing breaks and short circuits
Solution Approach 1:
The patent applies composite materials by creating a layered electrode film structure consisting of multiple metal layers (e.g., aluminum-copper alloy layer combined with other metal layers). This composite structure prevents migration by combining materials with complementary properties, where the lowermost layer extends to side surfaces to form a barrier against migration while maintaining electrical conductivity and structural integrity under acoustic wave vibrations and heat.
Solution Approach 2:
The patent segments the electrode film into multiple functional layers, with each layer having specific thickness and material composition. The lowermost layer is segmented to extend to the side surfaces of the electrode, creating a stepped structure that provides migration prevention at critical edges while maintaining the overall electrode functionality.
2Reliability
If the second electrode film is made thicker to reduce wiring resistance, then electrical conductivity improves, but migration becomes more severe due to increased material volume subject to vibration and heat
Solution Approach 1:
The patent applies local quality by making the lowermost layer extend to the side surfaces of the electrode structure, providing enhanced migration prevention at the vulnerable edge regions. The layer thickness is locally optimized: thicker at the sides for migration prevention, and sufficient thickness in the center for conductivity, creating a non-uniform but functionally optimized structure.
Solution Approach 2:
The patent transitions from a two-dimensional planar electrode film to a three-dimensional stepped structure by extending the lowermost layer to the side surfaces. This dimensional change creates a protective barrier that addresses migration in the vertical dimension while maintaining the horizontal electrical connectivity, effectively using the third dimension to solve a two-dimensional problem.
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 solution prevents breaks and short circuits in wiring electrodes, ensuring reliable operation even at elevated temperatures, thereby enhancing the durability and performance of acoustic wave devices.
Implementation Method 1
the lowermost layer of the layered metal film defining the second electrode film is made of a metal selected from the group consisting of aluminum-copper alloy, nickel-chromium alloy, aluminum-silicon alloy, aluminum-titanium alloy, titanium, and copper, and the lowermost layer of the layered metal film defining the second electrode film is arranged to extend to a side surface of the second electrode film
Data Source
AI summary
An acoustic wave device includes a first electrode film arranged on a top surface of a piezoelectric substrate and defining electrodes including IDT electrodes and a second electrode film arranged to extend from the top surface of the piezoelectric substrate to a portion of a top surface of the first electrode film. The second electrode film defines electrodes including a wiring electrode 9 and pad electrodes and is made of a layered metal film including a plurality of metal films deposited in layers. The lowermost layer of the second electrode film is made of a metal selected from the group consisting of aluminum-copper alloy, nickel-chromium alloy, aluminum-silicon alloy, aluminum-titanium alloy, titanium, and copper, and the lowermost layer of the second electrode film is arranged to extend to a side surface of the second electrode film.