SAW Composite Substrate Intervening Layer for Spurious Suppression
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Solution Overview
Problem
Surface acoustic wave filters using composite substrates experience energy leakage and noise issues due to acoustic wave trapping, leading to increased loss and spurious components, which deteriorate frequency characteristics.
Innovation Solution
A composite substrate design incorporating a piezoelectric single crystal thin film, a support substrate, and an intervening layer with specified thickness and attenuation properties, including SiOx or SiOyNz materials, to minimize wave trapping and enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a composite substrate with a low sound velocity medium is used, then the piezoelectric film can be made thinner, but acoustic wave energy leaks into the low velocity medium causing spurious noise and increased loss
Solution Approach 1:
A matching layer is introduced as an intermediary between the piezoelectric film and the low sound velocity medium. This matching layer has sound velocity and impedance properties that are intermediate between the two adjacent layers, serving as a transition that prevents acoustic wave energy from leaking into the low velocity medium while allowing the piezoelectric film to maintain its reduced thickness
2Object-generated harmful factors
If wave reflection at the interface is increased to suppress spurious, then pass band loss increases
Solution Approach 1:
The matching layer is designed to utilize the acoustic impedance difference at interfaces to create controlled reflections that suppress spurious components. By carefully selecting the sound velocity and thickness of the matching layer, the harmful wave reflections are converted into beneficial effects that eliminate spurious noise while maintaining low pass band loss
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 design reduces pass band loss and suppresses spurious components, ensuring high performance and reliability in surface acoustic wave devices.
Implementation Method 1
an attenuation of a longitudinal wave of the intervening layer as calculated by a Brillouin oscillation method at a frequency of 40 GHz to 60 GHz being 8 × 10 -2
Implementation Method 2
comb electrodes (IDT: Inter Digital Transducer) formed on a piezoelectric substrate to excite surface acoustic waves
Data Source
Figure 1~2
Figure 3
Figure 4~5(b)
AI summary
Provided is a composite substrate for surface acoustic wave devices, the composite substrate including a piezoelectric single crystal thin film, a support substrate, and at least one intervening layer that is provided between the piezoelectric single crystal thin film and the support substrate, the intervening layer being in contact with the piezoelectric single crystal thin film, the total thickness of the intervening layer being equal to or less than twice the wavelength of the surface acoustic wave, and the attenuation of a longitudinal wave of the intervening layer as calculated by a Brillouin oscillation method at a frequency of 40 GHz to 60 GHz being 8 × 10-2 (nm-1 · THz-2) or less. According to the present invention, it is possible to provide a composite substrate for surface acoustic wave devices, which has a small loss in the pass band of a filter, few spurious components, and excellent high performance and high reliability.