SAW Composite Substrate Structure for Spurious Noise Suppression
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Solution Overview
Problem
Surface acoustic wave filters experience noise issues due to energy leakage and reflection at the bonding interface between piezoelectric crystal films and supporting substrates, leading to deteriorated frequency characteristics and increased loss, and the pyroelectricity of single-crystal piezoelectric films is affected by temperature changes during the manufacturing process.
Innovation Solution
A composite substrate with a piezoelectric single crystal thin film and a support substrate, featuring a first intervening layer with a faster acoustic velocity than the piezoelectric film, and a second layer with a slower acoustic velocity, along with an uneven structure at the bonding interface, to trap and reflect elastic waves effectively, thereby minimizing noise and maintaining polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a composite substrate is formed by bonding a material with small thermal expansion coefficient to lithium tantalate or lithium niobate, then temperature characteristics are improved, but spurious noise is generated due to elastic wave leakage and reflection at the bonding interface
Solution Approach 1:
An intervening layer is introduced between the piezoelectric single crystal thin film and the support substrate. This intervening layer acts as an acoustic impedance matcher that prevents elastic wave leakage and reflection at the bonding interface, thereby eliminating spurious noise while maintaining the temperature stability benefits of the composite substrate structure.
Solution Approach 2:
The patent creates a multi-layer composite structure consisting of the piezoelectric single crystal thin film, the intervening layer with specific acoustic velocity properties, and the support substrate. This composite material approach allows simultaneous optimization of thermal expansion compensation and acoustic wave confinement.
2Device complexity
If the piezoelectric single crystal thin film is thinned to several μm, then the composite substrate structure is achieved, but polarization disturbance occurs due to temperature changes during manufacturing
Solution Approach 1:
The intervening layer is designed with specific acoustic velocity characteristics to preemptively protect the thin piezoelectric film from polarization disturbance during manufacturing processes. By controlling the acoustic impedance matching at interfaces, the structure prevents temperature-induced polarization changes before they can occur during subsequent manufacturing steps.
3Object-generated harmful factors
If an uneven structure is formed at the bonding interface, then spurious noise is reduced, but manufacturing precision requirements increase
Solution Approach 1:
Instead of relying on geometric unevenness at the bonding interface, the patent changes the acoustic velocity parameter of the intervening layer to achieve acoustic impedance matching. This parameter-based solution reduces spurious noise through material property optimization rather than geometric complexity, thereby lowering manufacturing precision requirements.
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 significantly reduces spurious noise and loss in the passband of surface acoustic wave filters, while maintaining the polarization of the piezoelectric single crystal film, even under temperature changes, resulting in improved frequency characteristics and stability.
Implementation Method 1
the acoustic velocity of the transverse wave in the first intervening layer is faster than the acoustic velocity of the fast transverse wave in the piezoelectric single crystal thin film
Implementation Method 2
a second intervening layer between the first intervening layer and the support substrate, the acoustic velocity of the transverse wave in the second intervening layer is slower than the acoustic velocity of the fast transverse wave in the piezoelectric single crystal thin film
Implementation Method 3
a piezoelectric single crystal thin film
Data Source
AI summary
A piezoelectric composite substrate for SAW devices with small loss is provided. A composite substrate for a surface acoustic wave device according to one embodiment of the present invention has a piezoelectric single crystal thin film, a support substrate, and a first intervening layer between the piezoelectric single crystal thin film and the support substrate. In said composite substrate, the first intervening layer is in contact with the piezoelectric single crystal thin film, and the acoustic velocity of the transverse wave in the first intervening layer is faster than the acoustic velocity of the fast transverse wave in the piezoelectric single crystal thin film.