SH-Wave Acoustic Structure Using 3C-SiC to Suppress Spurious Modes
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Solution Overview
Problem
Conventional acoustic wave devices using silicon carbide as a support substrate generate a large spurious response due to higher-order modes, which affect their performance.
Innovation Solution
The use of a silicon carbide substrate with a 3C—SiC cubic crystal structure and a lithium tantalate or lithium niobate layer, combined with a low acoustic velocity film, to excite an SH wave as a main mode, reduces or prevents higher-order modes by ensuring the acoustic velocity of the silicon carbide substrate is higher than that of the piezoelectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon carbide substrate is used as support substrate, then the acoustic wave device can be manufactured with good material properties, but a large spurious response is generated due to higher-order modes
Solution Approach 1:
The patent changes the crystal structure parameter of the silicon carbide substrate from conventional forms to the 3C-SiC cubic crystal structure. This parameter change modifies the acoustic wave propagation characteristics, enabling the substrate to support SH waves while suppressing higher-order modes that cause spurious responses, thus resolving the contradiction between device performance and spurious response generation
Solution Approach 2:
The patent creates a composite structure by combining the 3C-SiC cubic crystal structure substrate with a piezoelectric film layer. This composite material system leverages the unique properties of the cubic silicon carbide crystal structure to achieve both high reliability and suppression of harmful higher-order modes, as the specific crystal structure provides favorable acoustic impedance matching and wave propagation characteristics
2Productivity
If higher-order modes are present, then the acoustic wave device operates, but spurious response increases and performance deteriorates
Solution Approach 1:
The patent converts the potential harm of higher-order modes into a benefit by utilizing the specific acoustic wave propagation characteristics of the 3C-SiC cubic crystal structure. The crystal structure is designed such that SH waves are efficiently generated while higher-order modes are naturally suppressed, transforming what could be a harmful effect into a beneficial selective mode generation that improves device performance
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 minimizes higher-order modes, enhances the Q value, and increases the fractional bandwidth, thereby improving the overall performance of the acoustic wave device.
Implementation Method 1
a piezoelectric layer on the support substrate, and an IDT electrode on the piezoelectric layer
Implementation Method 2
ensuring the acoustic velocity of the silicon carbide substrate is higher than that of the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a support substrate, a piezoelectric layer on the support substrate, and an IDT electrode on the piezoelectric layer and including a plurality of electrode fingers. The support substrate is a silicon carbide substrate including a 3C-SiC cubic crystal structure. The piezoelectric layer is a lithium tantalate layer or a lithium niobate layer. An SH wave is used as a main mode.