Composite-Substrate SAW Structure for Guided Evanescent Waves
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Solution Overview
Problem
Surface acoustic wave devices based on composite substrates face limitations in miniaturization and efficiency due to the excitation of standing waves and non-guided acoustic energy, which restricts their operating frequencies and performance.
Innovation Solution
A surface acoustic wave device with a piezoelectric layer having regions with varying physical parameters, such as elasticity or dopant concentration, between electrode means, allowing for the modification of acoustic wave coupling and propagation, combined with a Bragg mirror for reduced energy loss and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a second harmonic SAW device with a single comb electrode is used, then the operating frequency can be doubled compared to traditional inter-digitated transducers, but the generated acoustic wave becomes a standing wave which reduces electromechanical coupling efficiency
Solution Approach 1:
The piezoelectric layer is designed with non-uniform physical parameters, specifically with regions between the electrode means having different properties (such as different thickness, material composition, or elastic constants) compared to regions underneath the electrode means. This local variation in quality creates conditions that convert the standing wave into a propagating evanescent wave, thereby improving electromechanical coupling efficiency while maintaining the high operating frequency advantage of the second harmonic mode
2Ease of manufacture
If the piezoelectric layer has uniform physical parameters, then the device structure is simple and easy to manufacture, but non-guided acoustic energy corresponding to volume modes is excited causing energy losses
Solution Approach 1:
The piezoelectric layer incorporates regions with different physical parameters located between the electrode means, creating local variations that guide acoustic energy propagation. These localized modifications act as acoustic waveguides that confine and direct the acoustic energy, preventing excitation of non-guided volume modes and reducing energy losses while maintaining overall manufacturing simplicity
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 design enables the propagation of evanescent acoustic waves in the longitudinal direction, reducing unwanted effects and improving the device's frequency range and performance by optimizing the coupling between bulk and standing acoustic waves.
Implementation Method 1
one or more inter-digitated transducers (IDTs) are used to convert acoustic waves to electrical signals and vice versa by exploiting the piezoelectric effect of certain materials
Implementation Method 2
A surface acoustic wave can be established on the substrate by electrically exciting the fingers
Implementation Method 3
further comprising a Bragg mirror comprising a plurality of layers of alternating impedance
Data Source
AI summary
A surface acoustic wave device comprising a base substrate, a piezoelectric layer and an electrode layer in between the piezoelectric layer and the base substrate, a comb electrode formed on the piezoelectric layer comprising a plurality of electrode means with a pitch p, defined asp=A, with A being the wavelength of the standing acoustic wave generated by applying opposite potentials to the electrode layer and comb electrode, wherein the piezoelectric layer comprises at least one region located in between the electrode means, in which at least one physical parameter is different compared to the region underneath the electrode means or fingers. A method of fabrication for such surface acoustic wave device is also disclosed. The physical parameter may be thickness, elasticity, doping concentration of Ti or number of protons obtained by proton exchange.