Interdigital Transducer Layout for Suppressing Transverse Mode Ripples
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Solution Overview
Problem
Existing acoustic wave devices with interdigital transducer electrodes of large thickness fail to suppress transverse mode ripples due to increased acoustic velocity in edge regions when the dielectric film thickness is increased, contrary to the intended reduction in acoustic velocity.
Innovation Solution
The acoustic wave device incorporates a piezoelectric substrate with a reverse velocity surface and an interdigital transducer electrode with a specific wavelength-normalized film thickness, where the dielectric film thickness in edge regions is thinner than in the central region, and the electrode material is chosen from Pt, W, Mo, Ta, Au, or Cu, ensuring the wavelength-normalized film thickness meets specific criteria to reduce acoustic velocity in edge regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the film thickness of the dielectric film in the edge regions is increased to reduce acoustic velocity, then the mass of the interdigital transducer electrode increases, but the acoustic velocity increases contrary to intention when the electrode has large thickness
Solution Approach 1:
The patent applies local quality by making the dielectric film thickness vary across different regions of the interdigital transducer electrode. Specifically, the edge regions have a first film thickness while the central region has a second film thickness that is greater than the first. This localized differentiation allows the edge regions to have sufficient mass for acoustic velocity reduction while the central region maintains appropriate acoustic characteristics, preventing the counterintuitive velocity increase that occurs when the entire electrode is made uniformly thick.
2Reliability
If the film thickness of the dielectric film is increased to reduce acoustic velocity, then the transverse mode suppression is improved, but the acoustic velocity in edge regions increases when the electrode has large thickness
Solution Approach 1:
The patent implements local quality by differentiating the dielectric film thickness between edge regions and central region. The edge regions have a thinner first film thickness that effectively reduces acoustic velocity in those specific areas, while the central region has a thicker second film thickness. This localized approach ensures that transverse mode suppression is achieved through the thinner edge regions without causing the unwanted acoustic velocity increase that would result from making the entire electrode uniformly thick.
3Speed
If the wavelength-normalized film thickness of the interdigital transducer electrode is increased, then the acoustic velocity reduction is achieved, but the transverse mode cannot be suppressed when the acoustic velocity in edge regions increases relatively
Solution Approach 1:
The patent resolves this contradiction by applying local quality through spatially varying dielectric film thickness. The edge regions have a first film thickness optimized for acoustic velocity reduction, while the central region has a greater second film thickness. This creates a wavelength-normalized film thickness distribution where the edge regions (with smaller normalized thickness) reduce acoustic velocity effectively, while the overall structure maintains the transverse mode suppression that would be lost if the entire electrode had uniformly large thickness.
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 the acoustic velocity in edge regions, thereby suppressing or preventing transverse mode ripples even with interdigital transducer electrodes of large thickness, enhancing the performance of acoustic wave devices.
Implementation Method 1
an acoustic wave device utilizing a Rayleigh wave... a piezoelectric substrate with a reverse velocity surface having an elliptic shape, an interdigital transducer electrode disposed on or above the piezoelectric substrate
Data Source
AI summary
In an acoustic wave device, an interdigital transducer electrode is disposed on a piezoelectric substrate with a reverse velocity surface having an elliptic shape, and a dielectric film is disposed to cover the interdigital transducer electrode. Assuming an electrode density (%) of the interdigital transducer electrode to be y (%) and a wavelength-normalized film thickness 100h/λ (%) of the interdigital transducer electrode to be x (%), the wavelength-normalized film thickness x of the interdigital transducer electrode takes a value not less than x satisfying y=0.3452x2−6.0964x+36.262 depending on the electrode density of the interdigital transducer electrode.