Piezoelectric Acoustic Wave Structure for Undesired Wave Suppression
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Solution Overview
Problem
Acoustic wave devices using thickness-shear mode bulk waves often generate undesired waves within or outside the pass band, degrading their electrical characteristics.
Innovation Solution
The design incorporates a piezoelectric layer made of lithium niobate or lithium tantalate with specific electrode configurations, including recesses and dielectric films, where the center thickness between electrodes is greater than the electrode thickness, and the electrode pitch is less than or equal to 0.5 times the center thickness, to suppress unwanted wave reflections and improve impedance frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thickness-shear mode bulk waves are used in acoustic wave devices, then the devices can operate at desired frequencies, but undesired waves are generated within or outside the pass band
Solution Approach 1:
The piezoelectric layer is designed with non-uniform thickness, where the thickness varies in different regions. Specifically, the thickness at the electrode regions (tp2) is different from the thickness in the regions between electrodes (tp1), creating local quality variations that suppress undesired wave generation while maintaining desired thickness-shear mode operation
Solution Approach 2:
The invention changes the thickness parameter of the piezoelectric layer from uniform to non-uniform distribution. By controlling the ratio tp1/tp2 and setting tp1/p ≤ 0.5, the device achieves suppression of undesired waves while maintaining proper thickness-shear mode bulk wave operation for the intended frequency range
2Object-affected harmful factors
If the piezoelectric layer thickness is increased to suppress wave reflections, then wave reflection is reduced, but the device size increases
Solution Approach 1:
Instead of uniformly increasing the piezoelectric layer thickness throughout the device, the invention applies local thickness variations. The thickness is optimized differently in electrode regions versus inter-electrode regions, achieving wave reflection suppression only where necessary while minimizing overall device volume
Solution Approach 2:
The invention addresses the wave reflection problem by introducing thickness variation in the vertical dimension (z-direction) rather than increasing the horizontal footprint. By creating a non-uniform thickness profile through recesses or protrusions, the device suppresses reflections without proportionally increasing overall device size
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 suppresses undesired waves, reducing ripple formation in frequency characteristics and preventing wave reflections, thereby enhancing the electrical performance of acoustic wave devices.
Implementation Method 1
An acoustic wave device using thickness-shear mode bulk waves as disclosed in U.S. Pat. No. 10,491,192 described below has recently been proposed. This acoustic wave device includes a pair of electrodes on a piezoelectric layer. The two electrodes in the pair face each other on the piezoelectric layer and are connected to different potentials. The application of an AC voltage across the electrodes excites thickness-shear mode bulk waves.
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer made of one of lithium niobate or lithium tantalate and including first and second main surfaces, and first and second electrode fingers on the first main surface of the piezoelectric layer. The first and second electrode fingers are adjacent electrodes. When a center thickness of the piezoelectric layer in a region between the first and second electrode fingers is denoted by tp1, and a center-to-center distance between the first and second electrode fingers is denoted by p, tp1/p is about 0.5 or less. When a thickness of the piezoelectric layer in a region where the first electrode finger is located is denoted by tp2, tp1> tp2.