Love Wave Acoustic Structure for Transverse Mode Suppression
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Solution Overview
Problem
Existing acoustic wave devices using Love waves struggle to sufficiently reduce or prevent spurious responses due to high-order transverse modes, despite previous designs aimed at minimizing such responses.
Innovation Solution
The acoustic wave device incorporates a piezoelectric body with an IDT electrode and dielectric films, where a mass-adding film is placed within the dielectric film's edge regions, optimizing the film thickness ratios to create low- and high-acoustic-velocity regions, thereby confining energy and reducing transverse mode spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the mass-adding film is positioned closer to the IDT electrode with optimized film thickness ratios, then the piston mode operation is enhanced and transverse mode spurious responses are reduced, but the device complexity increases due to additional film layers and positioning requirements
Solution Approach 1:
The patent applies local quality by creating distinct regions with different acoustic velocity characteristics within the dielectric film structure. Specifically, it forms a first low-acoustic-velocity region and a second low-acoustic-velocity region by positioning mass-adding films at specific locations (closer to the IDT electrode) with optimized thickness ratios (T1/(T1+T2) between 0.24-0.49). This localized modification of acoustic properties in specific regions effectively suppresses transverse mode spurious responses while maintaining overall device functionality.
Solution Approach 2:
The patent employs composite materials by combining the dielectric film with mass-adding films to create a structured composite layer. This composite structure consists of the dielectric film material integrated with mass-adding film material, forming a multi-layer composite that exhibits tailored acoustic velocity characteristics. The composite material approach enables precise control over acoustic wave propagation and effective suppression of unwanted transverse modes.
2Reliability
If dielectric films with specific thickness ratios are used to create low- and high-acoustic-velocity regions, then energy confinement is improved and spurious responses are reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness ratio parameter T1/(T1+T2) of the dielectric film to fall within the specific range of 0.24-0.49. This parameter optimization creates the desired acoustic velocity distribution, forming low-acoustic-velocity regions that confine energy effectively. By establishing this specific parameter range, the patent achieves reliable suppression of transverse mode spurious responses while providing clear manufacturing specifications.
3Reliability
If the mass-adding film is positioned inside the dielectric film closer to the IDT electrode, then transverse mode suppression is enhanced, but the ease of manufacture decreases due to more complex film deposition processes
Solution Approach 1:
The patent applies dimensionality change by utilizing the thickness dimension (z-direction) of the dielectric film to position the mass-adding film at a specific depth (T1/(T1+T2) between 0.24-0.49 from the IDT electrode surface). This vertical positioning in the thickness dimension creates the necessary acoustic velocity gradient for transverse mode suppression. The approach transforms a two-dimensional surface problem into a three-dimensional structured solution, enabling effective mode control through controlled deposition at specific thickness ratios.
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 transverse mode spurious responses, even during frequency adjustment, by ensuring the mass-adding film is positioned closer to the IDT electrode and utilizing specific dielectric film thicknesses, enhancing the piston mode operation.
Implementation Method 1
an acoustic wave device that utilizes a piston mode... an IDT electrode provided on the piezoelectric body... Love waves are utilized as acoustic waves
Implementation Method 2
A mass-adding film is provided inside the first dielectric film in the first edge region and the second edge region... an acoustic velocity in the first edge region and the second edge region is lower than an acoustic velocity in a center region
Data Source
AI summary
An acoustic wave device utilizes Love waves and includes a piezoelectric substrate (piezoelectric body), an IDT electrode provided on the piezoelectric substrate, and a first dielectric film that is provided on the piezoelectric substrate and covers the IDT electrode. A center region, first and second edge regions, and first and second gap regions are disposed in this order in the IDT electrode. A mass-adding film is provided inside the first dielectric film in the first edge region and the second edge region. When T1 is the film thickness of the portion of the first dielectric film located between the IDT electrode and the mass-adding film and T2 is the film thickness of the portion of the first dielectric film located between the mass-adding film and the surface of the first dielectric film on the opposite side from the piezoelectric substrate, T1/(T1+T2)<about 0.5.