Composite Substrate Bonding Layers for Thin Piezoelectric Films
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Solution Overview
Problem
Existing composite substrates used in piezoelectric devices face challenges in maintaining strong bonding between the piezoelectric material substrate and the supporting substrate, especially when the piezoelectric material substrate is thinned, leading to potential separation issues.
Innovation Solution
A composite substrate is developed with a supporting substrate made of quartz, a piezoelectric material substrate, and multiple amorphous layers between them. The first amorphous layer contains 10 to 30 atom % silicon atoms, and the second amorphous layer contains 1 to 10 atom % fluorine atoms. This configuration enhances bonding strength through surface activation by plasma irradiation and subsequent thermal treatment at 250° C or higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piezoelectric material substrate is thinned to improve device performance, then the coupling and Q value are improved, but the bonding strength between the piezoelectric material substrate and supporting substrate deteriorates, causing separation
Solution Approach 1:
An amorphous layer containing silicon and fluorine atoms is introduced as an intermediary between the piezoelectric material substrate and the supporting substrate. This intermediate layer enhances the bonding strength at the interface, allowing the piezoelectric substrate to be thinned without causing separation. The amorphous layer acts as a mediator that strengthens the bond between the two substrates.
Solution Approach 2:
The composition of the amorphous layer is controlled by adjusting the plasma treatment parameters, specifically the ratio of oxygen to fluorine-containing gas and the treatment time. By changing these parameters, the silicon and fluorine atom content in the amorphous layer is optimized to achieve maximum bonding strength, enabling thin substrate design while preventing separation.
2Ease of manufacture
If plasma activation is used to bond the supporting substrate and piezoelectric material substrate at low temperature, then the bonding process is simplified, but the bonding strength is insufficient when the piezoelectric material substrate is thinned
Solution Approach 1:
The plasma treatment parameters are optimized to create an amorphous layer with specific silicon and fluorine atom content. By adjusting the oxygen to fluorine-containing gas ratio and treatment time, the bonding strength is enhanced while maintaining the low-temperature bonding process. This parameter optimization allows strong bonding without requiring high temperature or complex multi-step processes.
Solution Approach 2:
The bonding interface is transformed into a composite structure consisting of the piezoelectric material substrate, the amorphous layer with specific composition, and the supporting substrate. This composite structure at the interface provides enhanced bonding strength compared to direct bonding, while the overall process remains simple and low-temperature.
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 improved bonding strength prevents separation of the piezoelectric material substrate from the supporting substrate even when the piezoelectric material substrate is thinned, thereby enhancing the performance and reliability of acoustic wave devices.
Implementation Method 1
irradiating a plasma containing at least one of oxygen gas and nitrogen gas onto a surface of said supporting substrate to generate an activated surface; irradiating a plasma containing at least one of oxygen gas and nitrogen gas onto a surface of said piezoelectric material substrate to generate an activated surface
Implementation Method 2
subjecting the bonded body to a thermal treatment at a temperature of 250° C. or higher and 350° C. or lower
Data Source
AI summary
A composite substrate includes a supporting substrate composed of quartz, a piezoelectric material substrate, a first amorphous layer present between the supporting substrate and piezoelectric material substrate, and a second amorphous layer present between the supporting substrate and first amorphous layer. The first amorphous layer contains 10 to 30 atom % of silicon atoms, and the second amorphous layer contains 1 to 10 atom % of fluorine atoms.