Acoustic Wave Electrode Layout to Prevent Piezoelectric Film Cracks
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Solution Overview
Problem
Cracks occur in the piezoelectric film located over a cavity during manufacturing or use in existing acoustic wave devices.
Innovation Solution
The acoustic wave device is designed with a support substrate featuring a recess, a piezoelectric film covering the recess to form a cavity, and a functional electrode with specific busbars and electrode fingers, ensuring that overlap regions are positioned either outside or inside the cavity to prevent cracks, with specific dimensions for points A2, B2, C2, and D2 relative to the cavity edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a piezoelectric film is located over a cavity to reduce device size, then device size is reduced, but cracks occur in the piezoelectric film during manufacturing or use
Solution Approach 1:
The electrode structure is designed with different regions having different functions: the overlap region is positioned to avoid the cavity area where cracks are likely to occur, while the non-overlap regions extend toward the cavity to maintain electrical connectivity. This local differentiation of electrode functionality resolves the contradiction by protecting the piezoelectric film from cracks while maintaining device compactness.
Solution Approach 2:
The electrode fingers and busbars are pre-configured with specific geometric relationships before the piezoelectric film is subjected to stress during manufacturing or use. The overlap region is deliberately positioned away from the cavity in advance, creating a stress-free zone that prevents crack formation before they can occur during subsequent manufacturing steps or operational conditions.
2Reliability
If the overlap region of electrode fingers is positioned away from the cavity, then cracks are prevented in the piezoelectric film, but device area increases
Solution Approach 1:
The invention optimizes the parameters of the electrode structure, specifically the dimensions and positioning of the overlap region relative to the cavity. By carefully controlling the distance parameters (xa, ya, xb, yb, xc, yc, xd, yd) to be greater than about 25 μm, the design achieves crack prevention while minimizing the area penalty through precise parameter optimization rather than arbitrary enlargement.
3Volume of moving object
If the piezoelectric film covers the cavity completely, then device size is minimized, but stress concentration causes cracks during manufacturing
Solution Approach 1:
The electrode structure serves as an intermediary element that mediates between the cavity structure and the piezoelectric film. By positioning the overlap region away from the cavity, the electrode acts as a buffer that prevents stress concentration from transmitting to the piezoelectric film during manufacturing processes, thereby preventing cracks while maintaining the compact cavity-covered design.
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 design significantly reduces the occurrence of cracks in the piezoelectric film, maintaining high Q factors and resonance characteristics while allowing for reduced device size without propagation loss.
Implementation Method 1
a piezoelectric film covering the recess of the support substrate and defining a cavity together with the recess
Data Source
AI summary
An acoustic wave device includes a piezoelectric film and an IDT electrode on the piezoelectric film. The IDT electrode includes first and second busbars, at least one first electrode finger, and at least one second electrode finger. When an overlap region is defined as a region in which the first and second electrode fingers overlap each other in an acoustic wave propagation direction, points A2, B2, C2, and D2, defined as follows, are all outside the cavity when, at the points A2, B2, C2, and D2, xa>about 25 μm, ya>about 25 μm, xb>about 25 μm, yb>about 25 μm, xc>about 25 μm, yc>about 25 μm, xd>about 25 μm, and yd>about 25 μm.