Stacked Piezoelectric Acoustic Wave Structure for Harmonic Control
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Solution Overview
Problem
Existing bulk acoustic wave resonators face challenges in inhibiting the excitation of unnecessary fundamental waves while maintaining high resonant frequencies, leading to potential breakage and variations in resonant frequency characteristics.
Innovation Solution
The use of a stacked piezoelectric layer configuration with rotated Y-cut lithium tantalate and lithium niobate substrates, where the spontaneous polarization directions are opposite, and the thickness of the lithium niobate layer is less than that of the lithium tantalate layer, to suppress fundamental wave excitation and enhance second-harmonic wave excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If piezoelectric layers with opposite spontaneous polarization directions are stacked to excite second-harmonic acoustic waves, then second-harmonic wave excitation is enhanced, but fundamental wave excitation occurs as an unwanted side effect
Solution Approach 1:
The patent applies local quality by making the two piezoelectric layers asymmetric in thickness while maintaining opposite spontaneous polarization directions. The first piezoelectric layer has a first thickness and the second piezoelectric layer has a second thickness that is different from the first thickness. This local asymmetry in thickness distribution allows the structure to preferentially excite second-harmonic acoustic waves while suppressing fundamental wave excitation, resolving the contradiction between enhancing second-harmonic power and eliminating harmful fundamental wave generation.
2Speed
If high resonant frequencies are pursued in bulk acoustic wave resonators, then resonant frequency is improved, but piezoelectric layer breakage and resonant frequency characteristic variations increase
Solution Approach 1:
The patent employs composite materials by stacking two different piezoelectric layers (first piezoelectric layer and second piezoelectric layer) with opposite spontaneous polarization directions and different thicknesses. This composite structure distributes mechanical stress more evenly across the piezoelectric assembly, reducing the risk of layer breakage. The asymmetric thickness design further optimizes stress distribution, enabling high resonant frequencies while maintaining reliability and reducing characteristic variations.
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 unnecessary fundamental wave excitation, inhibits piezoelectric layer breakage, and stabilizes resonant frequency characteristics, allowing for higher resonant frequencies and reduced manufacturing variations.
Implementation Method 1
a first piezoelectric layer that is a rotated Y-cut lithium tantalate substrate and has a first thickness; a second piezoelectric layer that is a rotated Y-cut lithium niobate substrate, is stacked on the first piezoelectric layer, has a second thickness that is less than the first thickness, and has a spontaneous polarization direction that is substantially opposite to a spontaneous polarization direction of the first piezoelectric layer
Implementation Method 2
By stacking piezoelectric layers with spontaneous polarization directions opposite to each other, it is possible to excite the second-harmonic acoustic wave. When the second-harmonic acoustic wave is used as the main mode, the fundamental wave becomes an unnecessary wave.
Data Source
AI summary
An acoustic wave device includes a first piezoelectric layer that is a rotated Y-cut lithium tantalate substrate and has a first thickness, a second piezoelectric layer that is a rotated Y-cut lithium niobate substrate, is stacked on the first piezoelectric layer, has a second thickness that is less than the first thickness, and has a spontaneous polarization direction that is substantially opposite to a spontaneous polarization direction of the first piezoelectric layer, a first electrode provided on an opposite surface of the first piezoelectric layer from the second piezoelectric layer, and a second electrode that is provided on an opposite surface of the second piezoelectric layer from the first piezoelectric layer, at least a part of the first piezoelectric layer and at least a part of the second piezoelectric layer being interposed between the first electrode and the second electrode.