Acoustic Wave Multiplexer Coating for Rayleigh Response Shifting
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Solution Overview
Problem
In acoustic wave devices using SH waves, the Rayleigh wave response often coincides with the pass band of other filters, leading to deteriorated bandpass characteristics, and existing methods to change design parameters of the IDT electrode to shift this response also alter the main mode frequency characteristics, making it difficult to independently manage the Rayleigh wave frequency.
Innovation Solution
A non-uniform thickness protection film is applied over the substrate and electrode fingers, with thicker intermediate portions between electrode fingers and thinner vicinity portions, allowing the frequency of the Rayleigh wave response to be varied without changing the main mode frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the design parameters of the IDT electrode are changed to shift the Rayleigh wave response frequency, then the Rayleigh wave response frequency can be adjusted, but the main mode frequency characteristics are also altered
Solution Approach 1:
The protection film is designed with non-uniform thickness, where the thickness varies in different regions (thinner near electrode fingers, thicker in intermediate regions). This local variation in film thickness allows selective influence on Rayleigh wave response frequency without affecting the main mode frequency characteristics, as each region's film thickness is optimized for its specific functional requirement
Solution Approach 2:
Instead of adjusting the Rayleigh wave response frequency by changing IDT electrode parameters (one-dimensional adjustment), the invention introduces a new degree of freedom by varying the protection film thickness in the thickness dimension. This allows independent control of Rayleigh wave frequency while maintaining the electrode design that determines main mode frequency characteristics
2Ease of manufacture
If a uniform thickness protection film is used, then the manufacturing process is simple, but the Rayleigh wave response frequency cannot be independently adjusted
Solution Approach 1:
The protection film transitions from uniform thickness to non-uniform thickness with specific thickness variations: thinner portions near electrode fingers and thicker portions in intermediate regions. This local quality variation enables independent adjustment of Rayleigh wave response frequency while maintaining compatibility with standard semiconductor manufacturing processes for forming non-uniform films
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 approach effectively shifts the Rayleigh wave response frequency away from the pass band of other filters while maintaining the main mode frequency characteristics, improving bandpass characteristics in multiplexers and other acoustic wave devices.
Implementation Method 1
a Rayleigh wave response is generated at a frequency that is approximately 0.75 times the frequency of the main mode
Implementation Method 2
an acoustic wave device using an SH wave as a main mode
Data Source
AI summary
An acoustic wave device includes a substrate, an interdigital transducer electrode including electrode fingers on a main surface of the substrate, and a protection film covering the main surface of the substrate, and side surfaces and upper surfaces of the electrode fingers. The protection film includes a portion covering the main surface of the substrate, an intermediate portion between two of the electrode fingers adjacent to each other, and a vicinity portion of the electrode fingers. The intermediate portion is thicker than the vicinity portion.