IDT Dielectric Film Layout for Piston-Mode Acoustic Wave Devices
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Solution Overview
Problem
Conventional acoustic wave devices have limited material options for achieving a piston mode, as the dielectric film used to increase acoustic velocity in the central range is typically restricted to silicon nitride, and materials like silicon oxide lower acoustic velocity, restricting the degree of freedom in material selection.
Innovation Solution
An acoustic wave device with a piezoelectric substrate and an IDT electrode, where a dielectric film with lower permittivity and density than the piezoelectric layer is strategically placed between the substrate and the electrode, allowing for increased acoustic velocity in the central range while maintaining lower velocities in adjacent ranges, thereby achieving a piston mode and suppressing transverse modes, with improved material flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon nitride film is used as the dielectric film to increase acoustic velocity in the central range, then a piston mode can be achieved and transverse mode is suppressed, but the material selection is limited and degree of freedom is reduced
Solution Approach 1:
The patent changes the key parameter of dielectric film material from the conventional silicon nitride to silicon oxide, which has different acoustic velocity characteristics. By adjusting the thickness of the silicon oxide film to 0.005λ to 0.02λ, the invention achieves the desired acoustic velocity distribution and piston mode without being limited to silicon nitride, thus improving material selection freedom while maintaining performance
Solution Approach 2:
The dielectric film is selectively applied only in the central range of the IDT electrode where the electrode fingers overlap, with a specific thickness range. This localized application with controlled thickness creates the necessary acoustic velocity difference between the central range and adjacent ranges, achieving piston mode while allowing flexible material choice
2Adaptability or versatility
If a silicon oxide film is used as the dielectric film, then material selection freedom is improved, but the acoustic velocity is lowered and piston mode cannot be achieved
Solution Approach 1:
The patent identifies and controls the critical parameter of dielectric film thickness, setting it to 0.005λ to 0.02λ. This specific thickness range compensates for the lower acoustic velocity of silicon oxide by optimizing the acoustic impedance matching, thereby achieving the desired acoustic velocity distribution and piston mode with silicon oxide material
Solution Approach 2:
The invention replicates the functional effect of high-acoustic-velocity materials (like silicon nitride) using silicon oxide by carefully controlling the film thickness. The optimized thickness of silicon oxide film produces equivalent acoustic velocity enhancement in the central range, achieving the same piston mode effect with a different material
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 enables the use of various dielectric materials beyond silicon nitride, enhancing the acoustic velocity in the central range and achieving a piston mode while suppressing transverse modes, thus improving the degree of freedom in material selection and performance.
Implementation Method 1
Permittivity and density of the dielectric film are lower than permittivity and density of the piezoelectric layer. When seen in plan view, the dielectric film is provided at a portion overlapping with the central range, and not provided at a portion overlapping with one of the first range and the second range.
Implementation Method 2
an acoustic wave device includes a piezoelectric substrate including a piezoelectric layer, an IDT electrode provided on the piezoelectric substrate
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate including a piezoelectric layer, an IDT electrode provided on the piezoelectric substrate and including electrode fingers, and a dielectric film between the piezoelectric substrate and the IDT electrode. A portion of the IDT electrode in which the electrode fingers overlap with each other when seen in a propagation direction of an acoustic wave is an intersecting range. The intersecting range includes a central range and a first range and a second range sandwiching the central range in an electrode finger extending direction. Permittivity and density of the dielectric film are lower than that of the piezoelectric layer. When seen in plan view, the dielectric film is provided at a portion overlapping with the central range, and not provided at a portion overlapping with one of the first range and the second range.