Tilted C-Axis Acoustic Wave Structure With Opposed IDT Fields
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Solution Overview
Problem
Acoustic wave devices with IDT electrodes on both surfaces of a piezoelectric film experience increased high-order nonlinear distortion when the crystal axis of the piezoelectric film is tilted with respect to the normal direction of the surfaces.
Innovation Solution
The acoustic wave device incorporates interdigitated comb-shaped IDT electrodes on both surfaces of the piezoelectric film, with opposite electric field directions between the busbars and electrode fingers, and a tilted crystal c-axis to reduce second-order nonlinear distortion by canceling out potential differences across the surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the crystal c-axis of the piezoelectric film is tilted with respect to the normal direction of the first and second main surfaces, then the resonance characteristics are improved, but the second-order nonlinear distortion increases
Solution Approach 1:
The patent applies asymmetry by configuring the IDT electrodes on the first and second main surfaces with different orientations relative to the crystal axes. Specifically, the IDT electrode on the first main surface has its electrode fingers extending in a direction that forms a different angle with the crystal a-axis compared to the IDT electrode on the second main surface. This asymmetric configuration compensates for the distortion caused by crystal axis tilting, thereby reducing second-order nonlinear distortion while maintaining improved resonance characteristics.
Solution Approach 2:
The patent employs the counterweight principle by designing the IDT electrodes to generate opposing electric field components that cancel out the unwanted second-order nonlinear distortion. The IDT electrodes are configured such that their electric field distributions create equal and opposite effects on the distortion components, effectively neutralizing the harmful nonlinear distortion while preserving the beneficial resonance characteristics enabled by crystal axis tilting.
2Volume of moving object
If IDT electrodes are provided on both surfaces of the piezoelectric film, then the device size can be reduced, but high-order nonlinear distortion may be increased due to crystal axis tilting
Solution Approach 1:
The patent uses asymmetry to resolve the contradiction between compact device size and reduced nonlinear distortion. By configuring the IDT electrodes on opposite surfaces with different orientations relative to the crystal axes, the device maintains a compact form factor while the asymmetric electrode geometry compensates for distortion effects, enabling small size without suffering from increased high-order nonlinear distortion.
Solution Approach 2:
The patent applies dimensionality change by utilizing the three-dimensional space created by placing IDT electrodes on both surfaces of the piezoelectric film. This dual-surface configuration allows the device to achieve compact size by exploiting the thickness dimension, while the specific angular orientations of the electrodes in different dimensional planes work together to cancel distortion effects, resolving the contradiction between small size and low nonlinear distortion.
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 second-order nonlinear distortion and improves resonance characteristics, allowing for more efficient operation and potentially smaller device sizes by eliminating unwanted spurious responses.
Implementation Method 1
an acoustic wave device is known in which an IDT electrode is provided on each of opposing first and second main surfaces of a piezoelectric film... With the application of an opposite-phase AC voltage to the first and second IDT electrodes, a Lamb wave mainly formed of an SH-wave high-order mode is excited
Implementation Method 2
Each of the first and second IDT electrodes includes two comb-shaped electrodes interdigitated with each other... A direction of an electric field generated between the busbar and end portions of the electrode fingers facing the busbar
Data Source
AI summary
In an acoustic wave device, a first IDT electrode is provided on a first main surface of a piezoelectric film, and a second IDT electrode is provided on a second main surface of the piezoelectric film. A crystal c-axis of the piezoelectric film is tilted with respect to a direction normal to the first and second main surfaces. A direction of an electric field generated between a busbar of a comb-shaped electrode and end portions of electrode fingers facing the busbar in the first IDT electrode and a direction of an electric field generated between a busbar and end portions of electrode fingers facing the busbar in the second IDT electrode are opposite directions.