Acoustic Wave Filter Interconnect Structure Against Ion Migration
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Solution Overview
Problem
In acoustic wave devices, the migration of copper or silver ions from metal layers to the acoustic wave element can lead to degradation due to the piezoelectric substrate being easily charged, causing ion migration and potential short-circuits.
Innovation Solution
A thicker metal layer containing copper or silver is used to connect substrates, with a thinner conductive layer made of a component other than copper, silver, and tin, such as gold or aluminum, covering the side and upper surfaces to act as a barrier and prevent ion migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal layer containing copper or silver is used to connect substrates, then electrical conductivity is improved, but ion migration to the acoustic wave element occurs causing degradation
Solution Approach 1:
A first conductive layer is introduced as an intermediary barrier between the copper or silver metal layer and the acoustic wave element. This conductive layer prevents direct contact and ion migration while maintaining electrical connectivity, thus resolving the contradiction between using conductive metals and preventing ion migration damage.
Solution Approach 2:
The connection structure uses a composite material system combining a copper or silver metal layer with a separate conductive layer. This composite structure leverages the high conductivity of copper/silver while the conductive layer provides protection against ion migration, achieving both electrical performance and reliability.
2Strength
If a thicker metal layer is used to connect substrates, then mechanical strength is improved, but ion migration risk increases
Solution Approach 1:
The connection structure is segmented into functionally distinct layers: a thicker metal layer for mechanical strength and electrical conductivity, and a separate conductive layer for ion migration protection. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The conductive layer acts as an intermediary barrier that decouples the mechanical function (provided by the thick metal layer) from the protective function (preventing ion migration). This allows the metal layer to be thick for strength without directly increasing ion migration risk to the acoustic wave element.
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 suppresses the migration of copper or silver ions to the acoustic wave element, reducing the risk of degradation and maintaining device performance.
Implementation Method 1
copper or silver ions may migrate to the acoustic wave element
Data Source
AI summary
An acoustic wave device includes a first substrate, an acoustic wave element provided on a first surface of the piezoelectric layer, a second substrate, a first metal layer provided on the first surface and conductively connected to the acoustic wave element, a second metal layer provided on a second surface of the second substrate, a third metal layer that connects the first metal layer to the second metal layer, is thicker than the first metal layer and the second metal layer, and contains copper or silver, and a first conductive layer that covers a side surface of the third metal layer, and a third surface of the first metal layer in a region surrounding another region where the third metal layer is bonded to the first metal layer, is thinner than the third metal layer, and contains a component other than copper, silver, and tin as a main component.