Quartz-Piezoelectric Composite Substrate With Amorphous Bonding Layer
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Solution Overview
Problem
Existing composite substrates for 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 quartz supporting substrate and a piezoelectric material substrate made of lithium niobate, lithium tantalate, or their solid solution, incorporating an amorphous interface layer with high concentrations of hydrogen, nitrogen, and fluorine atoms. This interface layer is formed through plasma activation and subsequent thermal treatment at 250° C. or higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the piezoelectric material substrate is thinned to improve device performance, then the device performance is improved, but the bonding strength between the piezoelectric material substrate and supporting substrate decreases leading to separation
Solution Approach 1:
An interface layer is introduced between the piezoelectric material substrate and the supporting substrate to act as a mediator that enhances bonding strength. This interface layer contains hydrogen, nitrogen, and fluorine atoms at specific concentrations (1×10^18 to 5×10^21 atoms/cm³), creating strong chemical bonds that prevent separation even when the piezoelectric substrate is thinned to 20 μm or smaller.
Solution Approach 2:
The bonding strength is enhanced by changing the chemical composition parameters of the interface layer. Specifically, hydrogen, nitrogen, and fluorine atoms are introduced at controlled concentrations through plasma treatment and thermal processing, transforming the interface properties to achieve optimal bonding without requiring a thick piezoelectric substrate.
2Strength
If plasma activation and thermal treatment are applied to form an interface layer with high concentrations of hydrogen, nitrogen, and fluorine atoms, then the bonding strength is enhanced, but the manufacturing process complexity increases
Solution Approach 1:
Plasma activation is performed as a preliminary treatment before bonding to introduce hydrogen, nitrogen, and fluorine atoms into the interface region. This preliminary action prepares the surface for strong bonding by creating the necessary chemical environment, allowing the subsequent thermal treatment to effectively form the interface layer with the desired composition.
Solution Approach 2:
Thermal treatment at 250°C or higher induces phase transitions and atomic diffusion that concentrate hydrogen, nitrogen, and fluorine atoms at the interface. This thermal processing transforms the plasma-treated surface into a stable interface layer with enhanced bonding properties, utilizing temperature-driven atomic rearrangement to achieve the desired composition.
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 proposed solution significantly enhances the bonding strength between the piezoelectric material substrate and the supporting substrate, effectively preventing separation even when the piezoelectric material substrate is thinned to 20 μm or smaller, thus improving the performance and reliability of piezoelectric devices.
Implementation Method 1
irradiating a plasma containing nitrogen gas onto a surface of the supporting substrate to generate an activated surface
Implementation Method 2
irradiating a plasma containing nitrogen gas onto a surface of the piezoelectric material substrate to generate an activated surface
Implementation Method 3
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 composed of a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalate; and an interface layer along a bonding interface between the supporting substrate and the piezoelectric material substrate. The interface layer has amorphous structure and contains constituent components including silicon, oxygen and at least one of tantalum and niobium. The interface layer has concentrations of hydrogen atoms, nitrogen atoms and fluorine atoms of 1×1018 atoms/cm3 or higher and 5×1021 atoms/cm3 or lower, respectively.