Boundary Acoustic Wave Device With Ni-Diffused Au Electrode
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Solution Overview
Problem
Boundary acoustic wave devices face challenges in reducing insertion loss, particularly in their frequency characteristics and electric power withstanding performance, especially when used as resonators and filters.
Innovation Solution
The implementation of an IDT electrode structure with a Au layer and a Ni layer, where Ni is diffused from the Ni layer's surface into the Au layer, and optionally including a metal layer with Al, to enhance the electrode's performance by reducing insertion loss through improved adhesion and strain suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second electrode layer made of another metal material (e.g., Ti, Cr, or NiCr) is laminated on the electrode layer made of Au, Ag, Cu, or Al to improve adhesion and electric power withstanding performance, then adhesion and electric power withstanding performance are improved, but insertion loss is increased
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of Ni atoms within the Au layer. The Ni concentration is high at the surface (in contact with NiCr layer) and decreases toward the interior, providing local hardening and adhesion improvement at the surface while maintaining the bulk Au's low loss characteristics. This resolves the contradiction by improving surface properties without compromising overall electrical performance.
Solution Approach 2:
The patent creates a composite structure by diffusing Ni atoms into the Au layer, forming a composition gradient material. The surface region has higher Ni content for improved adhesion and power withstanding, while the interior maintains higher Au content for low loss. This composite approach allows simultaneous achievement of both improved reliability and reduced insertion loss.
2Loss of energy
If the Au layer surface is hardened by Ni diffusion to reduce insertion loss, then insertion loss is reduced, but the electrode structure becomes more complex
Solution Approach 1:
The patent applies preliminary action by performing Ni diffusion into the Au layer during the lamination process itself. The NiCr layer is laminated on the Au layer, and the subsequent heating treatment that bonds the layers also drives the Ni diffusion. This preliminary hardening action is built into the manufacturing process, avoiding the need for separate complex treatment steps.
Solution Approach 2:
The patent merges two functions into a single process: the lamination of the NiCr layer and the diffusion hardening of the Au layer surface occur together through the heating treatment required for bonding. This combination simplifies the overall process by eliminating the need for separate diffusion treatment steps, reducing manufacturing complexity while achieving the desired surface hardening.
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 reduces insertion loss by hardening the Au layer's surface, suppressing damping, and lowering electrical resistance, thereby improving the device's frequency characteristics and overall performance as a resonator or filter.
Implementation Method 1
a portion of Ni defining the Ni layer is diffused from the Ni layer side surface of the Au layer toward the inside of the Au layer
Data Source
AI summary
A boundary acoustic wave device includes a first medium, a second medium, and an IDT electrode disposed at an interface between the first medium and the second medium, the IDT electrode having an Au layer defining a main electrode layer, wherein a Ni layer is laminated so as to contact at least one surface of the Au layer, and a portion of Ni defining the Ni layer is diffused from the Ni layer side surface of the Au layer toward the inside of the Au layer.