Acoustic Wave Electrode Layout With Mass-Addition Films for Spurious Waves
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Solution Overview
Problem
Acoustic wave devices using bulk waves in the thickness-shear mode generate unnecessary waves at frequencies close to and lower than the resonant frequency, leading to degraded electrical characteristics.
Innovation Solution
The acoustic wave device incorporates a piezoelectric substrate with a support and a piezoelectric film, featuring an IDT electrode with busbars and electrode fingers. A mass-addition film is provided over specific edge and gap regions, with varying lengths to suppress unnecessary waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a bulk wave in thickness-shear mode is used to excite acoustic waves, then acoustic wave generation is achieved, but unnecessary waves are generated at frequencies close to and lower than resonant frequency
Solution Approach 1:
The invention uses mass-addition films to convert the harmful unnecessary waves into beneficial effects by suppressing spurious resonances through controlled mass distribution at specific locations (edge regions and gap regions), thereby eliminating the harmful frequency components while maintaining the desired acoustic wave generation
Solution Approach 2:
The invention applies different mass-addition film configurations to different regions of the IDT electrode structure - specifically distinguishing between edge regions (where electrode fingers meet the busbar) and gap regions (spaces between electrode fingers). By controlling the mass distribution locally at these different positions with varying film thicknesses or materials, the invention selectively suppresses unnecessary waves at specific frequency ranges while preserving the main resonant mode
2Reliability
If mass-addition films are added to suppress unnecessary waves, then electrical characteristics are improved, but device structure becomes more complex
Solution Approach 1:
The invention controls the characteristics of mass-addition films by adjusting parameters such as film thickness, material composition, and spatial distribution patterns. By optimizing these parameters, the invention achieves effective suppression of unnecessary waves while maintaining a relatively simple overall device structure that can be integrated into existing acoustic wave device manufacturing processes
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 at frequencies close to and lower than the resonant frequency, thereby enhancing the electrical characteristics of the acoustic wave device.
Implementation Method 1
a piezoelectric layer provided on the support, and an IDT electrode, provided on the piezoelectric layer... A bulk wave in the thickness-shear mode is excited by an AC voltage being applied between the electrodes
Implementation Method 2
a first mass-addition film provided over the first edge region and the first gap region, and a second mass-addition film provided over the second edge region and the second gap region... reduce or prevent an unnecessary wave at frequencies close to and lower than the resonant frequency
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate that includes a support including a support substrate and a piezoelectric film including a piezoelectric layer on the support, and an IDT electrode, on the piezoelectric layer, that includes first and second busbars facing each other, and first and second electrode fingers. An acoustic reflection portion is located where the support overlaps the IDT electrode in plan view. When a thickness of the piezoelectric film is d and a center-to-center distance between the first and second electrode fingers adjacent to each other is p, d/p is about 0.5 or less. An overlap region is where the first and second electrode fingers adjacent to each other overlap in an electrode finger orthogonal direction and includes a middle region, and first and second edge regions on both sides of the middle region in an electrode finger extension direction.