Acoustic wave device, high frequency front end circuit, and communication apparatus
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Solution Overview
Problem
Existing acoustic wave devices suffer from spurious emissions due to the confinement of high-order modes, which deteriorate the device's characteristics by concentrating energy in the piezoelectric body, leading to unwanted spurious emissions.
Innovation Solution
The acoustic wave device incorporates a material layer and a piezoelectric body with specific Euler angles and elastic constants, where at least one elastic constant of the material layer and the piezoelectric body have opposite signs, allowing for the reduction or prevention of high-order modes by adjusting the Euler angles, particularly inverting the signs of elastic constants like C41, C42, and C56, and using a high acoustic velocity material layer and a low acoustic velocity film to control mode propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a piezoelectric body is laminated on a silicon substrate with an SiO2 film interposed therebetween, then the heat resistance is enhanced, but high-order modes are confined in the piezoelectric body causing spurious emissions
Solution Approach 1:
The patent changes the elastic constant parameters of the piezoelectric body by selecting specific crystal orientations (Euler angles) to invert the signs of elastic constants C41, C42, and C56. This parameter change modifies the acoustic wave propagation characteristics to prevent high-order mode confinement while maintaining heat resistance through the SiO2 film structure.
Solution Approach 2:
The patent uses a composite structure consisting of a silicon substrate, SiO2 film, and piezoelectric body with specific crystal orientations. This composite material system combines the heat resistance of SiO2 with the acoustic wave properties of the piezoelectric body, while the specific orientation configuration prevents spurious emissions by controlling mode propagation.
2Reliability
If the piezoelectric body is configured to concentrate energy in the main mode, then the main mode characteristics are improved, but high-order modes are also confined producing spurious emissions
Solution Approach 1:
The patent applies parameter changes by selecting specific Euler angles for the piezoelectric body to invert the signs of elastic constants C41, C42, and C56. This modifies the acoustic wave propagation to maintain main mode energy concentration while preventing high-order mode confinement, thereby eliminating spurious emissions without sacrificing main mode characteristics.
Solution Approach 2:
The patent inverts the signs of specific elastic constants (C41, C42, C56) by changing the crystal orientation of the piezoelectric body. This inversion fundamentally alters the acoustic wave propagation characteristics, reversing the typical mode confinement behavior to prevent spurious emissions while maintaining main mode 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 reduces or prevents high-order modes while maintaining the characteristics of the main mode, improving frequency-temperature characteristics and reducing spurious emissions, thereby enhancing the device's performance.
Implementation Method 1
a piezoelectric body made of a single crystal
Implementation Method 2
energy of the main mode as an acoustic wave
Data Source
AI summary
An acoustic wave device includes a material layer which has Euler angles and an elastic constant at the Euler angles, a piezoelectric body which includes first and second principal surfaces opposing each other, is laminated directly or indirectly on the material layer so that the second principal surface is on the material layer side and has Euler angles, and whose elastic constant at the Euler angles, and an IDT electrode which is disposed on at least one of the first principal surface and the second principal surface of the piezoelectric body. At least one elastic constant among elastic constants C11 to C66 of the material layer not equal to 0 and at least one elastic constant among elastic constants C11 to C66 of the piezoelectric body not equal to 0 have opposite signs to each other.