Bonded Substrate for SAW Devices with UV-Activated Covalent Interface
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Solution Overview
Problem
Current surface acoustic wave (SAW) devices face issues with high propagation attenuation and temperature coefficient variability, particularly in longitudinal-type leaky SAWs, which affect yield and performance in high-frequency and broadband operations.
Innovation Solution
A bonded substrate is created by covalently bonding a quartz substrate with a piezoelectric substrate, such as lithium tantalate or niobate, using an amorphous layer like silicon dioxide or aluminum oxide, and employing ultraviolet light irradiation under reduced pressure to enhance bonding strength and reduce temperature coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a proton exchange layer and reverse proton exchange layer are formed to reduce bulk wave radiation losses, then propagation characteristics are improved, but device yield becomes extremely poor
Solution Approach 1:
The patent extracts and eliminates the complex proton exchange layer structure from the substrate surface. Instead of forming proton exchange and reverse proton exchange layers, the invention uses a simple adhesive layer bonding the piezoelectric substrate to the supporting substrate, thereby avoiding the manufacturing complexity and low yield associated with proton exchange processes while maintaining effective suppression of bulk wave radiation
Solution Approach 2:
The patent changes the approach from chemical modification (proton exchange) to mechanical bonding (adhesive layer). By changing the parameter of substrate treatment from chemical etching to physical bonding, the invention achieves comparable propagation characteristics with significantly improved device yield and simpler manufacturing
2Ease of manufacture
If adhesive agents are used to bond substrates, then manufacturing is simplified, but bonding strength and temperature characteristics deteriorate
Solution Approach 1:
The patent uses a thin adhesive layer (1-10 μm) that serves its bonding function effectively without requiring excessive thickness or complex composition. The adhesive layer is designed to be sufficiently thin to minimize its negative impact on temperature characteristics while remaining thick enough to provide adequate bonding strength and ease of manufacture
Solution Approach 2:
The patent creates a composite structure consisting of the piezoelectric substrate, adhesive layer, and supporting substrate. This composite material approach combines the advantages of different materials: the piezoelectric substrate provides high propagation velocity and coupling factor, the adhesive layer provides bonding strength and ease of manufacture, and the supporting substrate provides temperature stability with near-zero temperature coefficient
3Speed
If lithium niobate substrate is used for high propagation velocity, then phase velocity increases, but temperature coefficient of frequency increases
Solution Approach 1:
The patent segments the temperature compensation function from the propagation function. The piezoelectric substrate (lithium niobate or lithium tantalate) is dedicated to providing high propagation velocity and coupling factor, while the supporting substrate (quartz or ceramic) is dedicated to providing temperature stability with near-zero temperature coefficient. This segmentation allows each substrate to optimize its specific function without compromise
Solution Approach 2:
The patent applies local quality by selecting different materials for different functional requirements: the piezoelectric substrate layer is optimized for high-speed wave propagation with high coupling factor, while the supporting substrate layer is optimized for temperature stability. Each layer has its own specific material properties tailored to its local function within the composite 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
This approach results in improved phase velocity, electromechanical coupling factor, and reduced propagation attenuation, enabling high-speed, high-coupling SAW modes with stable temperature characteristics for next-generation mobile communication devices.
Implementation Method 1
the quartz substrate and the piezoelectric substrate are covalently bonded at an interface
Implementation Method 2
irradiating a bonding surface of the quartz substrate and a bonding surface of the piezoelectric substrate with ultraviolet light under a pressure lower than atmosphere pressure
Implementation Method 3
heating to secure covalent bonding
Data Source
AI summary
A method of manufacturing a bonded substrate, which has a quartz substrate and a piezoelectric substrate bonded, includes irradiating a bonding surface of the quartz substrate and a bonding surface of the piezoelectric substrate with ultraviolet light under a pressure lower than atmosphere pressure. After the irradiation, the bonding surface of the quartz substrate and the bonding surface of the piezoelectric substrate are brought into contact. And the quartz substrate and the piezoelectric substrate are pressurized in a thickness direction to bond the bonding surfaces.