SAW Substrate Bonding and Vibration Diffusion for Filter Accuracy
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Solution Overview
Problem
SAW filters face accuracy issues due to temperature-induced expansion and contraction of piezoelectric substrates, and internal vibrations causing noise that hinder high-accuracy filtering.
Innovation Solution
A SAW device manufacturing method involving a piezoelectric ceramic substrate and a support substrate with a lower thermal expansion coefficient, where the piezoelectric substrate is polished and bonded to the support substrate, and a vibration diffusion layer is formed using a laser beam to diffuse internal vibrations, reducing noise and maintaining filtering accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a piezoelectric substrate is used in a SAW filter, then the filter can operate at RF frequencies, but the substrate expands and contracts due to temperature changes, causing failure of high-accuracy filtering
Solution Approach 1:
The patent bonds a piezoelectric substrate to a support substrate with different thermal expansion characteristics to form a composite structure. This composite substrate combines the piezoelectric properties needed for SAW filter operation with the thermal stability of the support substrate, resolving the contradiction between functionality and dimensional stability.
Solution Approach 2:
The patent explicitly addresses thermal expansion by selecting a support substrate whose thermal expansion coefficient compensates for the piezoelectric substrate's expansion and contraction. This thermal compensation mechanism maintains the overall substrate dimensions stable despite temperature changes, preserving filtering accuracy.
2Stability of the object's composition
If a thin piezoelectric substrate is bonded to a support substrate to suppress thermal expansion, then thermal stability is improved, but internal vibrations propagating inside the substrate and reflecting on the bottom surface become noise
Solution Approach 1:
The patent extracts or removes the harmful internal vibrations from the system by providing an acoustic release structure at the bottom surface of the support substrate. This structure allows the unwanted vibrations to escape or be dissipated rather than reflecting back into the piezoelectric substrate, thereby eliminating the noise problem while maintaining thermal stability.
Solution Approach 2:
The patent converts the harmful reflected vibrations into a beneficial outcome by designing the acoustic release structure to actively manage the vibration energy. Instead of allowing vibrations to reflect and create noise, the structure provides a controlled path for vibration dissipation, transforming the potential harm into a mechanism that protects the filter's performance.
3Length of stationary object
If the piezoelectric substrate thickness is reduced to a predetermined thickness, then the substrate becomes thinner and more manageable, but the substrate may become more susceptible to vibrations and noise
Solution Approach 1:
The patent uses the composite structure of piezoelectric substrate bonded to support substrate to achieve the desired thin profile while maintaining vibration resistance. The support substrate provides mechanical strength and vibration damping, allowing the piezoelectric layer to be thin for manageable dimensions without becoming overly susceptible to vibrations.
Solution Approach 2:
The support substrate acts as an intermediary between the thin piezoelectric substrate and the external environment. It provides mechanical support and vibration isolation, enabling the piezoelectric substrate to maintain a thin, manageable thickness while the support substrate absorbs and dampens vibrations that would otherwise affect the thin structure.
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 method effectively suppresses the reduction in filtering accuracy by minimizing the impact of temperature changes and internal vibrations, ensuring high-accuracy filtering performance.
Implementation Method 1
a vibration diffusion layer forming step of applying a laser beam to the stacked substrate in the condition where the focal point of the laser beam is positioned inside the piezoelectric ceramic substrate or inside the support substrate, the laser beam having a transmission wavelength to the piezoelectric substrate or the support substrate, after performing the grinding step, thereby forming a modified layer as a vibration diffusion layer inside the piezoelectric ceramic substrate or inside the support substrate
Implementation Method 2
the piezoelectric substrate such as a lithium tantalate substrate and a lithium niobate substrate may expand and contract due to temperature changes, causing a failure of high-accuracy filtering
Data Source
AI summary
A SAW device manufacturing method includes a piezoelectric ceramic substrate polishing step of polishing a first surface of the piezoelectric ceramic substrate, a support substrate polishing step of polishing a first surface of the support substrate, a bonding step of bonding the first surface of the piezoelectric ceramic substrate to the first surface of the support substrate to thereby form a stacked substrate, a grinding step of grinding a second surface of the piezoelectric ceramic substrate, and a vibration diffusion layer forming step of applying a laser beam to the stacked substrate in the condition where the focal point of the laser beam is positioned inside the piezoelectric ceramic substrate to thereby form a modified layer as a vibration diffusion layer inside the piezoelectric ceramic substrate.