Composite Substrate Interface Layer for Thin Piezoelectric Bonding
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Solution Overview
Problem
The existing composite substrates for piezoelectric devices face challenges in maintaining strong bonding strength when the piezoelectric material substrate is thinned, leading to potential separation from the supporting substrate, particularly in the case of quartz and lithium niobate or lithium tantalate-based materials.
Innovation Solution
A composite substrate is developed with a quartz supporting substrate and a piezoelectric material substrate, featuring an interface layer with an amorphous structure comprising silicon, oxygen, tantalum, and niobium, and high concentrations of hydrogen, nitrogen, and fluorine atoms, achieved through plasma activation and thermal treatment at specific temperatures to enhance bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piezoelectric material substrate is thinned to improve device performance, then the device can achieve better acoustic wave characteristics, but the bonding strength between the piezoelectric material substrate and supporting substrate decreases, causing separation
Solution Approach 1:
An interface layer is introduced between the piezoelectric material substrate and supporting substrate to act as a mediator. This interface layer, containing silicon, oxygen, tantalum, niobium, hydrogen, nitrogen, and fluorine, provides strong bonding to both substrates, enabling the piezoelectric substrate to be thinned without separation.
Solution Approach 2:
The interface layer is formed as a composite material system combining multiple elements (Si, O, Ta, Nb, H, N, F) with specific concentration ratios. This composite structure provides enhanced bonding strength compared to simple oxide layers, allowing thin piezoelectric substrates to maintain strong adhesion to the supporting substrate.
2Strength
If plasma activation and thermal treatment are applied to improve bonding strength, then the bonding strength increases, but the process complexity increases
Solution Approach 1:
Specific parameter ranges are established for plasma treatment (power 50-200W, time 1-10 minutes) and thermal treatment (temperature 200-400°C, time 1-10 minutes). By optimizing these parameters, strong bonding is achieved while controlling process complexity through defined operational windows rather than uncontrolled variations.
Solution Approach 2:
Plasma activation is performed as a preliminary step before bonding to activate the surfaces of both substrates. This preliminary action creates reactive surface groups that enhance subsequent bonding efficiency, allowing strong adhesion to be achieved with moderate thermal treatment rather than requiring extreme conditions.
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 significantly improves bonding strength, preventing separation of the piezoelectric material substrate from the supporting substrate even when thinned, as evidenced by high concentrations of hydrogen, nitrogen, and fluorine in the interface layer, resulting in a robust composite substrate suitable for acoustic wave devices.
Implementation Method 1
irradiating a plasma containing nitrogen gas onto a surface of the supporting substrate to generate an activated surface; irradiating a plasma containing nitrogen gas onto a surface of the 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
Figure 1(a)~1(b)
Figure 2(a)~2(b)
Figure 3(a)~3(c)
AI summary
(Object) In bonding a supporting substrate made of quartz and a piezoelectric material substrate composed of lithium tantalate or the like, the object is to improve the bonding strength to prevent the separation even when the piezoelectric material substrate is thinned. (Solution for the object) A composite substrate 7 or 7A includes a supporting substrate 4 composed of quartz, a piezoelectric material substrate 1 or 1A composed of a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalate; and an interface layer 5 along a bonding interface between the supporting substrate 4 and the piezoelectric material substrate 1 or 1A. The interface layer 5 has amorphous structure and contains constituent components including silicon, oxygen and at least one of tantalum and niobium. The interface layer 5 has concentrations of hydrogen atoms, nitrogen atoms and fluorine atoms of 1×101 8 atoms/cm 3 or higher and 5×102 1 atoms/cm3 or lower, respectively.