Acoustic Wave Filter Layout to Suppress Unnecessary Resonance Waves
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Solution Overview
Problem
Acoustic wave devices using bulk waves in the thickness shear mode experience unnecessary wave generation near resonant and anti-resonant frequencies when a mass addition film is provided in the edge region, leading to increased loss and deterioration in filter characteristics.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer of lithium tantalate or lithium niobate with an IDT electrode configuration, where mass addition films are strategically placed over edge regions and gap areas, avoiding overlap between adjacent electrode fingers to minimize unnecessary wave generation. This configuration includes busbars and electrode fingers with specific dimensions and orientations to optimize wave excitation and reduce leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a mass addition film is provided in the edge region of the IDT electrode, then loss deterioration is reduced or prevented, but unnecessary waves are generated in the vicinity of resonant and anti-resonant frequencies
Solution Approach 1:
The patent applies local quality by providing mass addition films only in specific regions (edge regions and gap regions) of the IDT electrode rather than uniformly across the entire electrode. This localized approach allows the mass addition to reduce loss in critical areas while avoiding the generation of unnecessary waves in other regions, thus resolving the contradiction between loss reduction and harmful wave generation.
2Loss of energy
If mass addition films are provided over the entire IDT electrode including between adjacent electrode fingers, then loss is reduced, but unnecessary waves are generated near resonant and anti-resonant frequencies
Solution Approach 1:
The patent segments the mass addition film placement into distinct regions: edge regions at the boundaries of the IDT electrode and gap regions between busbars, while deliberately excluding the regions between adjacent electrode fingers. This segmentation strategy allows loss reduction in critical areas while preventing the formation of unnecessary waves in the electrode finger regions, resolving the technical contradiction.
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 design effectively reduces or prevents unnecessary waves near resonant and anti-resonant frequencies, thereby minimizing loss and improving filter characteristics by controlling the placement and dimensions of mass addition films in the acoustic wave device.
Implementation Method 1
A piezoelectric layer is provided on a support. A pair of electrodes are provided on the piezoelectric layer. The pair of electrodes face each other on the piezoelectric layer, and are connected to mutually different potentials. An alternating current (AC) voltage is applied between the electrodes to excite the bulk wave in the thickness shear mode.
Implementation Method 2
In the pair of edge regions, a dielectric layer or the like is provided on the IDT electrode. In this manner, the piston mode is established by forming a plurality of regions having different acoustic velocities in the extending direction of the plurality of electrode fingers. In this manner, a transverse mode is reduced or prevented.
Data Source
AI summary
An acoustic wave device includes a support including a support substrate, a piezoelectric layer on the support, and an IDT electrode on the piezoelectric layer and including busbars and electrode fingers. In plan view when viewed in a lamination direction of the support and the piezoelectric layer, an acoustic reflector overlaps at least a portion of the IDT electrode on the support. When a thickness of the piezoelectric layer is defined as d and a center-to-center distance between the electrode fingers adjacent to each other is defined as p, d/p is about 0.5 or smaller. Mass addition films are located over at least one of pair of edge regions and a gap region adjacent to the edge region and aligned in an electrode finger facing direction. The mass addition films are not located on at least a portion between the adjacent electrode fingers.