Boundary Acoustic Wave Structure for Spurious Mode Suppression
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Solution Overview
Problem
Boundary acoustic wave devices with a three-media structure face issues with higher-order mode spurious responses, which are affected by the thickness of the silicon oxide film, leading to a trade-off with the temperature coefficient of frequency (TCF).
Innovation Solution
A boundary acoustic wave device is designed with a piezoelectric substrate, a first medium layer of SiO2 or SiON, and a second medium layer of SiON or other materials with different acoustic velocities, where the acoustic velocity of the second medium layer is greater than that of the first medium layer, ensuring Va>V1, thereby preventing higher-order mode spurious responses without reducing the thickness of the first medium layer and improving temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the thickness of the silicon oxide film is reduced to suppress higher-order mode spurious responses, then the spurious responses are reduced, but the absolute value of the temperature coefficient of frequency (TCF) is increased
Solution Approach 1:
The patent changes the acoustic velocity parameter of the first medium layer by selecting materials (LiNbO3, LiTaO3, SiO2, SiON) with specific acoustic velocity characteristics. By controlling the acoustic velocity relationship (Va>V1) rather than simply adjusting film thickness, the patent suppresses higher-order mode spurious responses while maintaining acceptable TCF characteristics.
Solution Approach 2:
The patent employs a composite three-media structure combining piezoelectric substrate (LiNbO3 or LiTaO3) with dielectric layers (SiO2 or SiON). This composite structure allows optimization of acoustic velocity distribution across layers to suppress spurious responses while managing temperature coefficient effects through material selection rather than thickness reduction alone.
2Object-generated harmful factors
If the thickness of the first medium layer is reduced to prevent higher-order mode spurious responses, then spurious responses are suppressed, but the waveguide effect is weakened
Solution Approach 1:
The patent changes the acoustic velocity parameter relationship between layers (Va>V1) as the primary control mechanism rather than relying solely on thickness reduction. This parameter optimization suppresses spurious responses while preserving the waveguide effect by maintaining appropriate acoustic velocity gradients that guide boundary acoustic waves along the interface.
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 prevents higher-order mode spurious responses and reduces the absolute value of the temperature coefficient of frequency (TCF), enhancing the device's performance and stability across temperature changes without compromising the thickness of the first medium layer.
Implementation Method 1
an interdigital electrode (not shown) is arranged on a piezoelectric substrate 1001
Implementation Method 2
By forming the polycrystalline silicon film, as shown in FIG. 8, the boundary acoustic wave energy excited by the IDT electrode is confined in the first medium layer 1002 made of polycrystalline silicon oxide
Data Source
AI summary
A boundary acoustic wave device includes a first medium layer made of a first dielectric material and a second medium layer made of a second dielectric material having an acoustic velocity different from the acoustic velocity of the first dielectric material. The first medium layer and the second medium layer are disposed on a piezoelectric substrate, and an IDT electrode is arranged along the interface between the piezoelectric substrate and the first medium layer. When the fast transverse bulk wave of the piezoelectric substrate has an acoustic velocity V1 and a higher-order mode boundary acoustic wave has an acoustic velocity Va at an anti-resonance point, the boundary acoustic wave device satisfies the relationship Va>V1.