Acoustic Wave Membrane Structure for Crack Detection Stability
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Solution Overview
Problem
Existing acoustic wave devices face challenges in detecting cracks in membrane portions, which can lead to increased susceptibility to breakage and difficulty in identifying early-stage cracks due to propagation loss and reduced Q values during downsizing.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer made of lithium niobate or lithium tantalate with a support substrate and a functional electrode that overlaps with a space portion, along with structures having a smaller coefficient of thermal linear expansion, allowing for effective detection of cracks by altering the membrane portion's expansion and enhancing resonance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the acoustic wave device is downsized, then the device size is reduced, but propagation loss increases and Q values decrease making crack detection difficult
Solution Approach 1:
The patent utilizes bulk waves in the first-order thickness-shear mode that propagate through the piezoelectric layer, creating mechanical vibration that is sensitive to cracks in the membrane portion. This vibration mode allows for effective crack detection even in downsized devices by maintaining high Q values and low propagation loss through the specific wave mode and material properties.
Solution Approach 2:
The patent changes the wave propagation mode from surface acoustic waves to bulk waves in the first-order thickness-shear mode, and selects specific piezoelectric materials (lithium niobate or lithium tantalate) with appropriate acoustic wave velocities. These parameter changes enable the device to maintain high detection sensitivity despite size reduction.
2Reliability
If structures with smaller coefficient of thermal linear expansion are added, then crack detection capability is improved, but device complexity increases
Solution Approach 1:
The patent incorporates structures with a smaller coefficient of thermal linear expansion than the piezoelectric body layer. These structures create thermal stress differences that enhance the sensitivity of crack detection by causing differential expansion/contraction that amplifies the effect of cracks on wave propagation, allowing detection without complex additional sensing mechanisms.
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 enables easy detection of cracks in the membrane portion while maintaining high resonance characteristics and preventing propagation loss, even during downsizing, by utilizing a bulk wave in the first-order thickness-shear mode without the need for reflectors.
Implementation Method 1
a piezoelectric body layer provided on one main surface of the support substrate
Implementation Method 2
at least one structure on the piezoelectric body layer and having a smaller coefficient of thermal linear expansion than the piezoelectric body layer
Implementation Method 3
utilizing a bulk wave in the first-order thickness-shear mode without the need for reflectors
Data Source
AI summary
An acoustic wave device includes a support substrate including a space portion, a piezoelectric body layer on the support substrate, a functional electrode on the piezoelectric body layer and at least partially overlapping with the space portion in plan view along a lamination direction of the support substrate and the piezoelectric body layer, and a structure on the piezoelectric body layer and having a smaller coefficient of thermal linear expansion than the piezoelectric body layer. The structure includes a region located in a region of the piezoelectric body layer other than a region where the functional electrode is provided and that does not overlap with the space portion in the plan view.