Love-Wave SAW Substrate Composition for Stable TCF and Lower Material Cost
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Solution Overview
Problem
The existing surface acoustic wave devices using Love-wave-type SH waves face challenges in obtaining high-quality langasite crystals with high crystal uniformity and stable raw material supply due to the use of rare earth elements, leading to high material costs and instability in temperature characteristics.
Innovation Solution
A surface acoustic wave device utilizing a piezoelectric substrate formed from Ca3Ta(Ga1-xAlx)3Si2O14 single crystal with an Al interdigital electrode, where the normalized film thickness of the electrode is set to 0.16 or less, generating a Love-wave-type SH wave with a temperature coefficient of frequency (TCF) of 0, thereby eliminating the need for rare earth elements and ensuring stable raw material supply at a lower cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If langasite crystal substrate is used to achieve temperature characteristic with zero temperature coefficient of delay time, then temperature stability is improved, but material cost increases and raw material supply stability deteriorates due to use of rare earth element La
Solution Approach 1:
The patent changes the material parameters by substituting rare earth element La with non-rare earth elements (Ga, Al, Si) in the crystal structure. The composition Ca3Ta(Ga1-xAlx)3Si2O14 maintains the necessary piezoelectric and acoustic properties while eliminating dependence on rare earth elements, thereby reducing material cost and improving supply stability without sacrificing temperature stability.
Solution Approach 2:
The patent replaces expensive langasite crystal containing rare earth element La with a cheaper alternative material Ca3Ta(Ga1-xAlx)3Si2O14 that does not require rare earth elements. This substitution uses more abundant and economically viable materials while maintaining the functional performance of the surface acoustic wave device.
2Reliability
If langasite crystal with high crystal uniformity is used, then temperature characteristic stability is improved, but manufacturing difficulty increases due to difficulty in obtaining high-quality crystals
Solution Approach 1:
The patent modifies the crystal composition parameters by using Ca3Ta(Ga1-xAlx)3Si2O14 instead of langasite. This compositional change enables better crystal growth characteristics and higher crystal uniformity, making it easier to manufacture high-quality substrates with stable temperature characteristics while reducing the difficulty of obtaining high-quality crystals.
3Power
If interdigital electrode film thickness is increased to improve electromechanical coupling, then coupling efficiency is improved, but temperature coefficient of frequency stability deteriorates when normalized film thickness exceeds 0.16
Solution Approach 1:
The patent optimizes the electrode film thickness parameter by specifying that the normalized film thickness (film thickness divided by wavelength) should be 0.16 or less. This parameter optimization achieves the best balance between electromechanical coupling efficiency and temperature coefficient of frequency stability, ensuring both high power transfer and frequency stability across temperature variations.
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 solution provides a surface acoustic wave device with a stable temperature coefficient of frequency and efficient electromechanical coupling, achieving a cost-effective and reliable raw material supply by using a Ca3Ta(Ga1-xAlx)3Si2O14 single crystal substrate and optimizing the interdigital electrode film thickness.
Implementation Method 1
an interdigital electrode formed on a surface of the piezoelectric substrate, formed from Al, and configured to generate a Love-wave-type SH wave on the surface of the piezoelectric substrate
Implementation Method 2
The Love-wave-type SH wave has long been known as a surface wave that exists only in a specific propagation direction on a piezoelectric substrate and concentrates the energy of a bulk acoustic wave having only a shear wave component near the substrate surface
Data Source
AI summary
A surface acoustic wave device includes a piezoelectric substrate formed from a Ca3Ta(Ga1-xAlx)3Si2O14 single crystal, and an interdigital electrode formed on the surface of the piezoelectric substrate and formed from Al. The interdigital electrode is configured to generate a Love-wave-type SH wave on the surface of the piezoelectric substrate. A normalized film thickness obtained by dividing the film thickness of the interdigital electrode by the wavelength of the Love-wave-type SH wave is 0.16 or less.