Quartz Composite Substrate Bonding for Thinned Piezoelectric Layers
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Solution Overview
Problem
Existing composite substrates face challenges in maintaining strong bonding strength when the piezoelectric material substrate is thinned, leading to separation issues.
Innovation Solution
A composite substrate design with a supporting substrate of quartz, a piezoelectric material substrate, and amorphous layers containing specific compositions of silicon and fluorine atoms, achieved through plasma surface activation and thermal treatment at controlled temperatures.
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 decreases and separation occurs
Solution Approach 1:
An amorphous layer containing 10 to 30 atom% silicon atoms is introduced as an intermediary between the piezoelectric material substrate and the supporting substrate. This intermediate layer enhances bonding strength through chemical interaction, allowing the piezoelectric substrate to be thinned while preventing separation.
Solution Approach 2:
The composition of the amorphous layer is controlled to contain specific concentrations of silicon atoms (10-30 atom%). By adjusting the compositional parameter of the intermediate layer, optimal bonding strength is achieved while maintaining the thinned substrate structure.
2Temperature
If plasma activation is used to enable low temperature bonding, then bonding can be performed at 400°C, but the bonding strength is insufficient for thinned substrates
Solution Approach 1:
The amorphous silicon-containing layer serves as a mediator that enhances bonding strength beyond what plasma activation alone can achieve. This intermediate layer provides additional bonding mechanisms that strengthen the interface between thinned substrates.
Solution Approach 2:
The bonding interface becomes a composite structure combining plasma-activated surfaces with an amorphous silicon-containing layer. This composite bonding structure achieves both low-temperature processing and high bonding strength required for thinned substrates.
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 enhances bonding strength, preventing separation of the piezoelectric material substrate even when thinned, ensuring robust performance in 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
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) When a piezoelectric material substrate is bonded with a supporting substrate made of quartz, the object is to improve the bonding strength to prevent the separation even in the case that the piezoelectric material substrate is thinned. (Solution) A composite substrate 7 or 7A includes a supporting substrate 4 composed of quartz, a piezoelectric material substrate 1 or 1A, a first amorphous layer 5 present between the supporting substrate 4 and piezoelectric material substrate 1 or 1A, and a second amorphous layer 11 present between the supporting substrate 4 and first amorphous layer 5. The first amorphous layer 5 contains 10 to 30 atom% of silicon atoms, and the second amorphous layer 11 contains 1 to 10 atom% of fluorine atoms.