Acoustic Wave Element IDT Electrode Geometry Optimization
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Solution Overview
Problem
The edge reflection type acoustic wave element faces challenges in manufacturing due to the narrow width of electrode fingers required for high-frequency signals, making it difficult and costly to produce, while traditional elements with reflectors are bulky and loss-prone.
Innovation Solution
The acoustic wave element design includes a piezoelectric substrate with an IDT and an end face where the distance between the inner end of the electrode finger and the end face is optimized within specific ranges relative to the wavelength and metallization ratio, allowing for wider electrode fingers and reduced bulk radiation, thus improving manufacturability and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the width of electrode fingers is reduced to accommodate high-frequency signals, then the acoustic wave element can operate at high frequencies, but the manufacturing difficulty and cost increase significantly
Solution Approach 1:
The patent changes the geometric parameters of the IDT, specifically setting the width of electrode fingers to be 1/4 wavelength or more and the distance between adjacent electrode fingers to be 1/4 wavelength or more. This parameter optimization allows high-frequency operation while maintaining manufacturable dimensions, resolving the contradiction between high frequency capability and ease of manufacture
Solution Approach 2:
The patent uses electrode fingers with width equal to or greater than 1/4 wavelength, which is larger than the minimum theoretical requirement. This excessive dimension ensures easy manufacturing while still achieving the desired high-frequency performance, trading some dimensional precision for manufacturing ease
2Speed
If the width of electrode fingers is reduced to accommodate high-frequency signals, then the acoustic wave element can operate at high frequencies, but the manufacturing cost increases
Solution Approach 1:
The patent optimizes the geometric parameters of the IDT electrode fingers, setting both the width and spacing to be 1/4 wavelength or more. This parameter selection enables high-frequency operation while maintaining dimensions that are easy and inexpensive to manufacture, directly resolving the cost-frequency trade-off
3Reliability
If a reflector is used to reflect the acoustic wave, then the acoustic wave element can function properly, but the device size increases and bulk wave loss occurs
Solution Approach 1:
The patent extracts and eliminates the reflector component from the acoustic wave element design. Instead of using a separate reflector structure, the invention uses the optimized IDT electrode configuration itself to achieve the necessary acoustic wave control, thereby reducing device size while maintaining functionality
Solution Approach 2:
The IDT structure is designed to serve multiple functions: it not only generates the acoustic wave but also provides the reflection function that would traditionally require a separate reflector component. This multi-functionality reduces the overall device size while maintaining acoustic wave reflection capability
4Reliability
If a reflector is used to reflect the acoustic wave, then the acoustic wave element can function properly, but bulk wave loss increases
Solution Approach 1:
The patent removes the reflector component that causes bulk wave loss. The optimized IDT electrode configuration directly controls the acoustic wave without generating the harmful bulk waves that occur between the IDT and reflector in traditional designs, thereby reducing energy loss
Solution Approach 2:
The patent converts the potential harmful effect of bulk wave generation into a benefit by optimizing the electrode geometry. The specific width and spacing of 1/4 wavelength or more prevent bulk wave formation while maintaining effective acoustic wave reflection, turning a potential loss mechanism into a low-loss 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 enables the acoustic wave element to maintain high Q-values and reduce bulk radiation loss, facilitating the production of acoustic wave elements for high-frequency signals while minimizing fabrication complexity and cost.
Implementation Method 1
an IDT (Interdigital Transducer) formed on the piezoelectric substrate
Implementation Method 2
an end face of the piezoelectric substrate that is formed on at least one end of the IDT in a propagation direction of an acoustic wave
Data Source
AI summary
An acoustic wave element includes: a piezoelectric substrate; an IDT (Interdigital Transducer) formed on the piezoelectric substrate; and an end face of the piezoelectric substrate that is formed on at least one end of the IDT in a propagation direction of an acoustic wave; wherein when a wavelength of the acoustic wave which the IDT excites is expressed by “λ” and a metallization ratio of the IDT is expressed by “D”, a distance between an inner end of an electrode finger of the IDT nearest to the end face and the end face is equal to or more than 7λ/16+D×λ/4 and equal to or less than 3λ/4+D×λ/4.