SAW Layer Structure for Temperature-Stable Spurious Mode Suppression
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Solution Overview
Problem
Earlier surface acoustic wave (SAW) devices using lithium tantalite and lithium niobate piezoelectric layers suffer from poor temperature stability and generate spurious modes due to the thickness of the piezoelectric layer.
Innovation Solution
A SAW device with a substrate having protrusions, an intermediate layer filling the recess among these protrusions, and a piezoelectric layer on top, which includes a substrate made of sapphire and an intermediate layer of silicon dioxide to mitigate temperature-induced frequency drift and spurious modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the piezoelectric layer thickness is reduced to improve temperature stability, then temperature stability is improved, but spurious modes are generated
Solution Approach 1:
The patent introduces protrusions at specific locations on the substrate surface, creating local structural variations. These protrusions are strategically positioned to suppress spurious modes only in the regions where they occur, without affecting the overall thin piezoelectric layer design that provides temperature stability.
Solution Approach 2:
The protrusions act as intermediary structures between the substrate and the piezoelectric layer. They modify the acoustic wave propagation path and suppress spurious modes through their geometric configuration, while allowing the thin piezoelectric layer to maintain its temperature stability benefits.
2Measurement precision
If a thin piezoelectric layer is used to compensate frequency drift, then frequency drift compensation is improved, but spurious modes are generated above resonance frequency
Solution Approach 1:
The protrusions create localized structural modifications that specifically target spurious mode suppression. The non-uniform distribution of protrusions addresses the spurious mode problem in specific frequency regions without compromising the overall frequency drift compensation achieved by the thin piezoelectric layer.
Solution Approach 2:
The substrate surface is segmented into multiple regions with and without protrusions. This segmentation allows different areas to serve different functions: regions with protrusions suppress spurious modes, while the overall thin piezoelectric layer structure maintains frequency drift compensation across the device.
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 effectively suppresses spurious modes while maintaining high Q factor and temperature stability, improving the performance of the SAW device.
Implementation Method 1
an earlier-developed surface acoustic wave (SAW) device includes a piezoelectric layer 11, and an electrode layer 12 that is disposed on the piezoelectric layer 11 and that includes an interdigital electrode
Implementation Method 2
the substrate 13 is made of sapphire (Al2O3), which could inhibit expansion of the piezoelectric layer 11 physically
Data Source
AI summary
A surface acoustic wave device includes a substrate that has a top surface and that contains a plurality of protrusions protruding from the top surface and spaced apart from each other, an intermediate layer disposed on the substrate so as to fill a recess formed among the protrusions, a piezoelectric layer disposed on the intermediate layer opposite to the substrate, and an electrode layer disposed on the piezoelectric layer opposite to the intermediate layer.