Guided SAW Structure for Spurious Mode Rejection
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Solution Overview
Problem
Conventional Surface Acoustic Wave (SAW) devices with guided SAW structures face issues with spurious mode generation above the resonance frequency, which hinders their practical use due to unsatisfied out-of-band rejection specifications.
Innovation Solution
A SAW device with a guided SAW structure that includes a non-semiconductor support substrate, a piezoelectric layer, and at least one interdigitated transducer, where the thickness of the piezoelectric layer and the acoustic wave velocity of the support substrate are optimized to suppress spurious modes by ensuring the frequency of these modes is above the bulk wave cut-off frequency, thereby improving the quality factor, electromechanical coupling, and thermal coefficient of frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a guided SAW structure is used to improve device performance, then quality factor and electromechanical coupling are enhanced, but spurious modes are generated above resonance frequency
Solution Approach 1:
The patent changes the physical parameters of the piezoelectric layer by controlling its thickness to be less than two times the wavelength (λ) of the resonance frequency. This parameter change shifts the spurious mode frequencies above the bulk wave cut-off frequency, thereby suppressing spurious modes while maintaining the guided SAW structure's quality factor and electromechanical coupling benefits.
Solution Approach 2:
The patent applies local quality by creating a specific thickness region in the piezoelectric layer that is optimized for spurious mode suppression. The thickness is controlled to be less than 2λ, which creates a localized condition that suppresses spurious modes above the resonance frequency while allowing the guided SAW structure to function properly at the resonance frequency.
2Power
If piezoelectric layer thickness is increased to improve coupling, then electromechanical coupling increases, but spurious mode frequency decreases below cut-off frequency
Solution Approach 1:
The patent optimizes the piezoelectric layer thickness parameter to be less than two times the wavelength (λ) of the resonance frequency. This specific parameter range achieves the right balance: it provides sufficient electromechanical coupling for device operation while ensuring that spurious mode frequencies remain above the bulk wave cut-off frequency for effective suppression.
3Volume of moving object
If conventional guided SAW structure is used, then device size is reduced, but out-of-band rejection specifications are not satisfied
Solution Approach 1:
The patent changes the thickness parameter of the piezoelectric layer to be less than two times the wavelength (λ), which shifts the spurious mode frequencies above the bulk wave cut-off frequency. This parameter change enables the compact guided SAW structure to satisfy out-of-band rejection specifications by suppressing spurious modes, thereby resolving the contradiction between device size reduction and out-of-band rejection 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
The proposed solution effectively suppresses spurious modes above the resonance frequency, enhancing the performance of SAW devices by maintaining higher quality factor, electromechanical coupling, and thermal coefficient of frequency while avoiding bulk radiation losses.
Implementation Method 1
a piezoelectric layer on a surface of the non-semiconductor support substrate, and at least one interdigitated transducer (IDT) on a surface of the piezoelectric layer
Implementation Method 2
a frequency of spurious modes above a resonance frequency of the SAW device is above a bulk wave cut-off frequency of the SAW device. In this manner, the spurious modes above the resonance frequency of the SAW device are suppressed.
Data Source
AI summary
Embodiments of a Surface Acoustic Wave (SAW) device having a guided SAW structure that provides spurious mode suppression and methods of fabrication thereof are disclosed. In some embodiments, a SAW device includes a non-semiconductor support substrate, a piezoelectric layer on a surface of the non-semiconductor support substrate, and at least one interdigitated transducer on a surface of the piezoelectric layer opposite the non-semiconductor support substrate. A thickness of the piezoelectric layer, a SAW velocity of the piezoelectric layer, and an acoustic velocity of the non-semiconductor support substrate are such that a frequency of spurious modes above a resonance frequency of the SAW device is above a bulk wave cut-off frequency of the SAW device. In this manner, the spurious modes above the resonance frequency of the SAW device are suppressed.