Acoustic Wave Filter Structure for Third Harmonic Excitation
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Solution Overview
Problem
Existing acoustic wave devices, such as surface acoustic wave filters, struggle with the excitation of unnecessary fundamental waves alongside the desired third harmonic wave, leading to inefficiencies and degraded filter characteristics.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer with inverted polarization directions and IDT electrodes having a duty ratio greater than 0.6, utilizing a structure with two lithium niobate layers and specific Euler angles to enhance the excitation of the third harmonic wave while minimizing the fundamental wave.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surface acoustic wave filter uses a LiTaO3 substrate with IDT electrodes to operate at third harmonic wave, then the third harmonic wave is excited, but the fundamental wave is also strongly excited and cannot be sufficiently suppressed
Solution Approach 1:
The piezoelectric layer is divided into multiple layers (first piezoelectric layer and second piezoelectric layer) with opposite polarization directions. This segmentation allows selective suppression of the fundamental wave while maintaining third harmonic wave excitation, resolving the contradiction between achieving third harmonic operation and suppressing fundamental wave interference.
Solution Approach 2:
Different regions of the piezoelectric layer are assigned different polarization directions (upward in the first layer, downward in the second layer). This local quality variation enables the structure to differentially affect fundamental and third harmonic waves, suppressing the harmful fundamental wave while preserving the desired third harmonic operation.
2Power
If the duty ratio of IDT electrodes is increased to enhance third harmonic wave excitation, then the third harmonic wave is better excited, but the fundamental wave suppression becomes more challenging
Solution Approach 1:
The IDT electrodes are designed with an asymmetric duty ratio of 0.6 or higher, deviating from the conventional 0.5 duty ratio. This asymmetric design, combined with the multi-layer piezoelectric structure with opposite polarizations, creates differential coupling that enhances third harmonic excitation while suppressing fundamental wave generation.
Solution Approach 2:
The duty ratio parameter of the IDT electrodes is changed from the conventional value to 0.6 or higher. This parameter change, when combined with the opposite polarization configuration of the piezoelectric layers, shifts the resonant characteristics to favor third harmonic excitation while suppressing fundamental wave interference.
3Device complexity
If a single-layer piezoelectric structure is used with IDT electrodes, then the device structure is simple, but the fundamental wave cannot be effectively suppressed
Solution Approach 1:
The piezoelectric layer is segmented into multiple layers with opposite polarization directions, transforming a simple single-layer structure into a multi-layer configuration. This segmentation enables the structure to generate opposing piezoelectric fields that cancel fundamental wave effects while preserving third harmonic excitation.
Solution Approach 2:
The polarization direction of the piezoelectric layers is inverted between layers (first layer upward, second layer downward). This inversion creates a push-pull effect that selectively suppresses the fundamental wave while maintaining third harmonic wave excitation, resolving the contradiction between structural simplicity and fundamental wave suppression.
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 excites the third harmonic wave and suppresses the fundamental wave, improving the filter characteristics and reducing unnecessary wave interference, thereby enhancing the performance of the acoustic wave device.
Implementation Method 1
a piezoelectric layer on the support substrate and including at least one lithium niobate layer
Implementation Method 2
IDT (interdigital transducer) electrodes on the first principal surface of the piezoelectric layer, and a second IDT electrode on the second principal surface
Data Source
AI summary
An acoustic wave device includes a support substrate, a piezoelectric layer on the support substrate, and at least one lithium niobate layer and first and second principal surfaces opposed to each other, and first and second IDT electrodes respectively on the first and second principal surfaces. Each of the first and second IDT electrodes includes electrode fingers. A duty ratio of each of the first and second IDT electrodes is equal to or greater than about 0.6. Directions of polarization of the piezoelectric layer are inverted in a thickness direction of the piezoelectric layer.