Composite Substrate with Argon-Graded Amorphous Layer
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Solution Overview
Problem
Existing composite substrates for surface acoustic wave devices face issues with insufficient bonding strength, leading to potential peeling during device fabrication and concerns about long-term reliability due to differences in thermal expansion coefficients between materials.
Innovation Solution
A composite substrate is created with a single crystal support substrate, an oxide single crystal layer, and an amorphous layer containing argon (Ar) with specific concentration gradients, enhancing bonding strength through Ar segregation and concentration in the amorphous layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heat treatment is applied to increase bonding strength, then bonding strength is improved, but warping, peeling, or cracking occurs due to difference in thermal expansion coefficients
Solution Approach 1:
An amorphous layer is introduced as an intermediary between the piezoelectric material layer and the support substrate. This amorphous layer has a composition gradient that transitions from piezoelectric material-rich near the piezoelectric layer to support substrate-rich near the support substrate, creating a gradual transition in thermal expansion coefficients that reduces thermal stress and prevents warping, peeling, and cracking during heat treatment.
2Reliability
If room temperature bonding is used to avoid thermal expansion issues, then substrate integrity is maintained, but sufficient bonding strength cannot be acquired
Solution Approach 1:
The composition parameters of the amorphous layer are precisely controlled to achieve optimal bonding strength. The amorphous layer contains specific ratios of first element (from piezoelectric material), second element (from support substrate), and third element, with the composition varying gradually through the layer thickness. This parameter optimization enables strong bonding while maintaining substrate integrity.
3Adaptability or versatility
If lithium tantalate or lithium niobate is used to increase bandwidth, then bandwidth is improved, but temperature stability deteriorates due to high thermal expansion coefficient
Solution Approach 1:
A composite structure is created consisting of the piezoelectric material layer (lithium tantalate or lithium niobate) bonded to a support substrate with lower thermal expansion coefficient through an amorphous transition layer. This composite structure combines the high electromechanical coupling coefficient and bandwidth capability of lithium tantalate/niobate with the thermal stability of the support substrate, achieving both high bandwidth and temperature stability.
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 achieves improved bonding strength between the single crystal support substrate and the oxide single crystal layer, ensuring reliable bonding and supporting thin-film piezoelectric devices with enhanced thermal stability.
Implementation Method 1
an amorphous layer provided in between the single crystal support substrate and the oxide single crystal layer and containing the first element, the second element, and Ar, the amorphous layer having a first amorphous region in which proportion of the first element is higher than proportion of the second element, and a second amorphous region in which the proportion of the second element is higher than the proportion of the first element, concentration of the Ar contained in the first amorphous region being higher than concentration of the Ar contained in the second amorphous region and being 3 atom % or more
Data Source
AI summary
A composite substrate includes a single crystal support substrate containing first element as a main component; an oxide single crystal layer provided on the single crystal support substrate and containing a second element (excluding oxygen) as a main component; and an amorphous layer provided in between the single crystal support substrate and the oxide single crystal layer and containing a first element, a second element, and Ar, the amorphous layer having a first amorphous region in which proportion of the first element is higher than proportion of the second element, and a second amorphous region in which the proportion of the second element is higher than the proportion of the first element, concentration of Ar contained in the first amorphous region being higher than concentration of Ar contained in the second amorphous region and being 3 atom % or more.