Single-Crystal SAW Film on Crystalline Substrate for Thermal Stability
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Solution Overview
Problem
Current surface elastic wave devices face challenges in achieving high quality coefficients and temperature stability, with existing substrates like lithium tantalate and lithium niobate experiencing significant thermal stress and frequency drift, limiting their application as frequency sources.
Innovation Solution
A hybrid substrate is created by combining a thin piezoelectric film with a substrate of high acoustic quality, where the piezoelectric film is thinner than 20 μm and in direct contact with the substrate, minimizing viscoelastic absorption and allowing elastic waves to propagate without energetic losses, thereby enhancing the quality factor and coupling coefficient while reducing temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium tantalate or lithium niobate substrates are used to achieve high electromechanical coupling coefficient, then the coupling coefficient is improved, but frequency temperature stability deteriorates due to substantial thermal stress and frequency drift
Solution Approach 1:
The patent employs a composite substrate structure consisting of a piezoelectric film layer (such as quartz, lithium niobate, or lithium tantalate) deposited on a non-piezoelectric substrate (such as silicon, glass, or ceramic). This composite configuration allows the piezoelectric film to provide high electromechanical coupling coefficient while the underlying substrate provides thermal stability and mechanical support, thereby resolving the contradiction between coupling efficiency and temperature stability
Solution Approach 2:
The patent modifies the physical and chemical parameters of the substrate system by controlling the thickness of the piezoelectric film (typically 1-20 μm), the composition of the substrate, and the deposition conditions. By adjusting these parameters, the device achieves optimal balance between electromechanical coupling and thermal stability, enabling high-performance resonators with Qf > 10,000 at frequencies of a few hundred MHz to a few GHz
2Reliability
If piezoelectric film thickness is increased to improve electromechanical coupling, then coupling coefficient is improved, but viscoelastic absorption increases reducing quality factor
Solution Approach 1:
The patent optimizes the thickness of the piezoelectric film to a specific range (1-20 μm) where the electromechanical coupling coefficient is sufficiently high while viscoelastic absorption remains low. This precise parameter control allows the device to achieve high quality factors (>10,000) by minimizing energy loss through the film while maintaining effective coupling
Solution Approach 2:
The patent introduces an intermediate substrate layer between the piezoelectric film and the final substrate, which acts as a mediator to reduce viscoelastic absorption. This intermediate layer helps to decouple the piezoelectric film from the substrate, reducing energy loss while maintaining the beneficial coupling effects
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 configuration results in improved quality coefficients and reduced temperature sensitivity, enabling the production of surface elastic wave devices with enhanced performance and stability, suitable for applications requiring high frequency accuracy and compactness.
Implementation Method 1
SAW devices are generally produced by depositing metal electrodes in the form of a network of interdigitated combs on a piezoelectric material
Implementation Method 2
the first material and the second material have viscoelastic coefficients lower than or equal to those of quartz for the propagation mode induced by the exciting means
Data Source
AI summary
A surface elastic wave device comprises a stack including: a thin film made of a piezoelectric first material; a substrate made from a second material; and exciting means for generating at least one surface acoustic wave propagation mode in the piezoelectric film; wherein: the first material is a single-crystal material and the second material is a crystalline material, the thickness of the thin film of piezoelectric first material being smaller than or equal to 20 μm, and the first material and the second material having viscoelastic coefficients lower than or equal to those of quartz for the propagation mode induced by the exciting means.