Acoustic Wave Filter Structure for Electrode-Finger Leakage Control
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Solution Overview
Problem
Acoustic wave devices experience leakage of acoustic waves due to the arrangement direction of electrode fingers, as described in Japanese Unexamined Patent Application Publication No. 2022-524136 and U.S. Pat. No. 11,349,450.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer with a protective film that includes a surface step exposing its side surface in a direction intersecting the electrode finger, with d/p ratio of 0.5 or less, and a support with an acoustic reflection portion to reduce or prevent wave leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrode fingers are arranged in a conventional configuration, then the device structure is simple, but acoustic wave leakage occurs in the arrangement direction
Solution Approach 1:
The protective film is segmented into multiple regions with different thicknesses, creating a stepped structure. This segmentation allows different portions of the film to serve different functions: thicker portions provide acoustic reflection while thinner portions allow electrode functionality, thereby containing acoustic waves without significantly increasing device complexity
Solution Approach 2:
The protective film exhibits local quality variations through its stepped thickness configuration. Specific regions have optimized thickness values tailored to their functional requirements, with the film being thicker in acoustic reflection zones and thinner in electrode interaction zones, thus improving acoustic wave containment while maintaining device simplicity
2Power
If the piezoelectric layer thickness d is large relative to electrode pitch p, then stronger acoustic wave generation occurs, but acoustic wave leakage increases
Solution Approach 1:
The invention optimizes the d/p ratio parameter to be 0.5 or less, fundamentally changing the dimensional relationship between piezoelectric layer thickness and electrode pitch. This parameter optimization ensures that acoustic wave generation remains effective while the stepped protective film structure simultaneously prevents leakage, resolving the contradiction between power and reliability
3Volume of moving object
If device size is reduced, then integration density improves, but resonance characteristics and Q value deteriorate
Solution Approach 1:
The invention addresses device size reduction by utilizing the vertical dimension through the stepped protective film structure. Instead of horizontally expanding to maintain resonance characteristics, the solution vertically segments the protective film into multiple thickness levels, allowing compact device footprint while preserving acoustic wave containment and Q value through the multi-level film configuration
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, maintains good resonance characteristics, and allows for a smaller device size without decreasing the Q value, while utilizing bulk waves in the first-order thickness-shear mode.
Implementation Method 1
a piezoelectric layer 20 including a first main surface 20a and a second main surface 20b
Implementation Method 2
a support 11 facing the second main surface 20b of the piezoelectric layer 20 and including an acoustic reflection portion 11R on a side adjacent to the second main surface 20b of the piezoelectric layer 20
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer including first and second main surfaces facing in a first direction, an IDT electrode on at least one of the first or second main surface and including electrode fingers arranged in an arrangement direction, a support facing the second main surface and including an acoustic reflection portion, and a protective film on at least one of the first or second main surface. In a region that overlaps, in plan view in the first direction, a first of the electrode fingers outermost in the arrangement direction, the protective film includes a surface of a first step where a side surface of the protective film is exposed in a direction intersecting an extending direction of the first electrode finger. When d is a thickness of the piezoelectric layer and p is a center-to-center distance between adjacent electrode fingers, d/p is about 0.5 or less.