Membrane Acoustic Wave Electrode Layout Without Reflectors
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Solution Overview
Problem
Acoustic wave devices face challenges in preventing cracks in the membrane portion, particularly during miniaturization, where propagation loss and reduced Q values occur due to the need for reflectors in traditional designs.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer made of lithium niobate or lithium tantalate with a support substrate having a hollow portion, where the electrode configuration includes an IDT electrode finger and an outer contour that intersects with the membrane portion's boundary, allowing for effective excitation of bulk waves in a thickness-shear primary mode without the need for reflectors, thereby preventing cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional acoustic wave device design with reflectors is used, then device structure is complete, but propagation loss increases and Q value decreases during miniaturization
Solution Approach 1:
The patent removes the reflector component from the acoustic wave device structure. By extracting the reflector, the device achieves miniaturization while maintaining high Q values and reducing propagation loss, as the reflector was causing energy dissipation and structural complexity.
Solution Approach 2:
Instead of using reflectors to define the acoustic wave propagation boundaries, the patent inverts the approach by using the electrode finger configuration itself to control wave propagation. The IDT electrode fingers are designed with specific dimensions and arrangements that inherently guide the acoustic waves without requiring additional reflector structures.
2Volume of moving object
If acoustic wave device is miniaturized, then device size decreases, but propagation loss increases and cracks occur in membrane portion
Solution Approach 1:
The patent extracts the reflector component that was causing stress concentration in the membrane portion. Without reflectors, the membrane structure remains intact during miniaturization, preventing cracks while reducing device size.
Solution Approach 2:
The patent changes the geometric parameters of the IDT electrode fingers, specifically setting the finger width to 0.05λ to 0.15λ and the pitch to 0.20λ to 0.40λ. These parameter optimizations enable effective acoustic wave excitation in miniaturized devices without causing membrane stress and cracks.
3Power
If IDT electrode finger dimensions are optimized, then bulk wave excitation efficiency increases, but manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes the IDT electrode finger dimensions with specific parameter ranges: finger width of 0.05λ to 0.15λ and pitch of 0.20λ to 0.40λ. These parameter ranges are designed to maximize bulk wave excitation efficiency while remaining manufacturable with standard fabrication tolerances.
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 enhances resonance characteristics, maintains high Q values even with miniaturization, and reduces propagation loss by utilizing bulk waves that propagate in the thickness-shear direction, preventing cracks in the membrane portion.
Implementation Method 1
a piezoelectric layer laminated on the support substrate and including a membrane portion at least partially overlapping the hollow portion in the lamination direction
Data Source
AI summary
An acoustic wave device includes a support substrate including a hollow portion, a piezoelectric layer laminated on the support substrate and including a membrane portion at least partially overlapping the hollow portion in a lamination direction, and an electrode on the piezoelectric layer. The electrode includes an IDT electrode finger and an electrode portion other than the IDT electrode finger. The IDT electrode finger is provided on the membrane portion, and an outer contour of the electrode portion intersects with a boundary of the membrane portion in plan view.