Acoustic Wave Electrode Cover Geometry for Unnecessary Wave Suppression
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Solution Overview
Problem
Acoustic wave devices with protective films suffer from unnecessary wave generation near resonant frequencies, which can deteriorate filter characteristics.
Innovation Solution
The design includes a piezoelectric substrate with a lithium tantalate or lithium niobate layer, functional electrodes, and a dielectric film that covers the electrodes, with specific geometrical features such as angled side surfaces and varying thicknesses of the dielectric film cover portions to minimize unnecessary wave generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective film is provided on the piezoelectric layer to cover the electrode, then the electrode is protected, but an unnecessary wave is generated near the resonant frequency which deteriorates filter characteristics
Solution Approach 1:
The dielectric film is designed with asymmetric thickness distribution: the first thickness in the first region is different from the second thickness in the second region. This asymmetric configuration creates different acoustic impedance conditions in different regions, which suppresses the generation of unnecessary waves while maintaining electrode protection. The asymmetry breaks the symmetry of wave generation that occurs with uniform protective films.
Solution Approach 2:
The protective film (dielectric film) is designed with spatially varying properties - different thicknesses in different regions (first region vs. second region). This local variation in film thickness creates localized acoustic impedance changes that selectively suppress unwanted waves at specific locations while maintaining the overall protective function. The local quality change allows the film to perform both protection and wave suppression functions simultaneously.
2Ease of manufacture
If the dielectric film has uniform thickness, then manufacturing is simplified, but unnecessary waves are generated that deteriorate filter characteristics
Solution Approach 1:
The dielectric film intentionally introduces asymmetry through different thicknesses in different regions. While this increases manufacturing complexity compared to uniform films, it provides the necessary acoustic impedance variation to suppress unnecessary waves. The asymmetric design is achieved through controlled deposition or etching processes that can create the required thickness profile.
Solution Approach 2:
The thickness parameter of the dielectric film is varied across different regions to achieve wave suppression. By changing the thickness parameter from a uniform value to a spatially varying value (first thickness in first region, second thickness in second region), the acoustic impedance is modified to prevent unnecessary wave generation while maintaining filter performance.
3Device complexity
If the acoustic wave device uses a simple structure without complex dielectric film variations, then device complexity is reduced, but filter characteristics are deteriorated due to unnecessary wave generation
Solution Approach 1:
The dielectric film incorporates local quality variations through different thicknesses in different regions. This localized variation provides the necessary acoustic impedance control to suppress unnecessary waves and maintain good filter characteristics. The structure remains relatively simple overall, with the complexity confined to the thickness variation of the dielectric film rather than requiring multiple separate components.
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 or prevents unnecessary waves near resonant frequencies, thereby improving the filter characteristics of acoustic wave devices.
Implementation Method 1
By applying an alternating-current (AC) voltage between the electrodes, the bulk wave in the thickness shear mode is excited
Implementation Method 2
an acoustic reflection portion is provided at a position overlapping at least a portion of the functional electrode in plan view
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate including a support that includes a support substrate, and a piezoelectric layer located on the support, a functional electrode located on the piezoelectric layer and including at least one pair of electrode fingers, and a dielectric film located on the piezoelectric layer to cover the at least one pair of electrode fingers. An acoustic reflection portion is located at a position overlapping at least a portion of the functional electrode in plan view. Assuming a thickness of the piezoelectric layer is d and a center-to-center distance between the electrode fingers adjacent to each other is p, d/p is about 0.5 or less. Angles of corners θ1, θ2, θ3, and θ4 are such that at least one of θ1≠θ3 or θ2≠θ4 is satisfied.