Acoustic Wave Filter Layout for IDT-End Leakage Suppression
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Solution Overview
Problem
Acoustic wave devices described in Japanese Unexamined Patent Application Publication No. 2022-524136 and U.S. Pat. No. 11,349,450 suffer from acoustic wave leakage in the arrangement direction of electrode fingers.
Innovation Solution
The acoustic wave devices and filter devices incorporate a piezoelectric layer with specific thickness and electrode finger spacing, along with a support and load film configurations that reduce or prevent acoustic wave leakage by utilizing a first-order thickness-shear mode bulk wave and minimizing the thickness ratio of the piezoelectric layer to electrode pitch, ensuring d/p is about 0.5 or less, and the distance between the electrode finger and load film is about 0.9 or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional acoustic wave device structure is used, then the device can operate with basic functionality, but acoustic wave leakage occurs in the arrangement direction of electrode fingers
Solution Approach 1:
The patent converts the harmful acoustic wave leakage into a beneficial reflected wave by introducing a reflective film that reflects acoustic waves in the arrangement direction of electrode fingers back into the active region, thereby improving acoustic wave containment and device performance
Solution Approach 2:
The patent adds a new dimensional element (the reflective film layer) to the existing acoustic wave device structure, creating a multi-layer configuration that addresses acoustic wave leakage without disrupting the original device architecture
2Reliability
If reflectors are added to prevent acoustic wave leakage, then acoustic wave containment improves, but device complexity and size increase
Solution Approach 1:
The reflective film serves multiple functions: it contains acoustic waves in the arrangement direction of electrode fingers, maintains device compactness, and can be integrated with existing device layers, thereby preventing acoustic wave leakage without significantly increasing device complexity
Solution Approach 2:
The patent optimizes specific parameters including setting the thickness of the piezoelectric layer to about one-quarter of the acoustic wave wavelength and positioning the reflective film at specific locations to achieve effective acoustic wave containment while maintaining device simplicity
3Reliability
If the piezoelectric layer thickness is increased to improve acoustic wave containment, then acoustic wave leakage reduces, but device size increases
Solution Approach 1:
The patent sets the piezoelectric layer thickness to about one-quarter of the acoustic wave wavelength, which is optimized to prevent acoustic wave leakage while maintaining compact device dimensions, avoiding the need for excessive thickness increases
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 effectively reduces or prevents acoustic wave leakage, enabling favorable resonance characteristics and size reduction without the need for reflectors, while maintaining a high Q factor and electromechanical coupling coefficient.
Implementation Method 1
a piezoelectric layer including a first major surface and a second major surface opposite to the first major surface, an IDT electrode on at least one of the first major surface and the second major surface of the piezoelectric layer
Implementation Method 2
a support facing the second major surface of the piezoelectric layer and including an acoustic reflection portion on a second major surface side of the piezoelectric layer
Implementation Method 3
a load film in a region that, in plan view in the first direction, overlaps at least one end portion of the IDT electrode in an arrangement direction of the plurality of electrode fingers
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer with first and second major surfaces, an IDT electrode on at least one of the first and second major surfaces and including electrode fingers arranged in a predetermined direction, a support facing the second major surface and including an acoustic reflection portion on the second major surface side, and a load film in a region that, in plan view in a first direction, overlaps at least one end portion of the IDT electrode in the arrangement direction. The end portion includes a first electrode finger positioned outermost in the arrangement direction, and d/p is about 0.5 or less where d is a thickness of the piezoelectric layer and p is a center-to-center distance between adjacent ones of the electrode fingers.