Elastic Wave Device Via Electrode Locking Section
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Solution Overview
Problem
Elastic wave devices face issues with via electrodes coming off the piezoelectric substrate due to weak bonding and differing thermal expansion coefficients, leading to detachment during temperature changes.
Innovation Solution
The design includes a via electrode with a locking section having a larger cross-sectional area than the through section, a rough surface contact with the wiring electrode, and a multilayer wiring electrode with a hard-to-etch layer, enhancing bonding strength and reducing electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the via electrode is bonded to the through hole simply by vapor deposition or sputtering, then the fabrication process is simple and fast, but the bonding strength between the via electrode and through hole is weak, causing the via electrode to come off easily
Solution Approach 1:
The via electrode is divided into multiple sections: a through section passing through the piezoelectric substrate, a locking section with enlarged cross-sectional area, and a bonding section. This segmentation allows different portions to serve different functions - the locking section provides mechanical interlocking while the bonding section provides electrical connection, resolving the contradiction between simple fabrication and strong bonding.
Solution Approach 2:
The via electrode transitions from a simple linear through-hole fill to a three-dimensional structure with varying cross-sectional areas. The locking section extends in the lateral dimension with a larger cross-sectional area than the through section, creating a mechanical lock that prevents detachment while maintaining fabrication efficiency through a single continuous deposition process.
2Device complexity
If the via electrode has a uniform cross-sectional area throughout, then the fabrication process is simple, but the via electrode can easily detach from the piezoelectric substrate under thermal stress
Solution Approach 1:
The via electrode exhibits local quality variations with different cross-sectional areas at different positions. The locking section has a locally enlarged cross-sectional area compared to the through section, providing enhanced mechanical interlocking capacity at the critical interface with the piezoelectric substrate while keeping other portions simpler, thus improving reliability without excessive overall complexity.
Solution Approach 2:
The via electrode structure is asymmetric with respect to its cross-sectional area distribution along its length. The locking section has a larger cross-sectional area than the through section, creating an asymmetric profile that provides directional mechanical locking capability, preventing detachment in the upward direction while maintaining fabrication simplicity.
3Ease of manufacture
If the contact surface between the via electrode and wiring electrode is smooth, then the fabrication process is simple, but the electrical resistance is higher and the bonding area is smaller
Solution Approach 1:
The locking section of the via electrode features a curved or rounded profile rather than sharp edges or flat surfaces. This curvature increases the contact area with the wiring electrode through better conformal contact while maintaining a relatively simple fabrication process, thereby improving electrical connection reliability without significantly complicating manufacturing.
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 significantly reduces the likelihood of via electrodes detaching from the piezoelectric substrate, maintaining electrical integrity and stability across temperature variations.
Implementation Method 1
the surface of the locking section in contact with the wiring electrode is a rough surface. This further increases the area of contact between the via electrode and wiring electrode, making the electrical resistance even lower.
Implementation Method 2
The via electrode includes a locking section at the one end, on the wiring electrode side. The locking section extends on the first primary surface of the piezoelectric body.
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate including first and second primary surfaces opposing one another, a via electrode extending through the piezoelectric substrate, and a wiring electrode on the first primary surface of the piezoelectric substrate. The via electrode is connected at one end to the wiring electrode, and the via electrode includes a locking section at the one end, on the wiring electrode side. The locking section extends on the first primary surface of the piezoelectric substrate.