Composite Wafer Bonding via Ion Implantation
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Solution Overview
Problem
Surface acoustic wave devices using lithium tantalate and lithium niobate materials face issues with temperature stability and spurious noise due to thermal expansion, and existing methods to mitigate these problems are either unreliable or costly.
Innovation Solution
A method involving ion implantation on the bonding surface of a supporting wafer with a low thermal expansion material, such as silicon or sapphire, to disturb crystallinity and reduce reflection, combined with surface activation treatments and insulating film formation to enhance bonding and suppress spurious noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thin LT film or LN film is stacked on a supporting substrate to suppress thermal expansion, then temperature characteristics are improved, but spurious noise occurs due to reflection from the interface
Solution Approach 1:
An ion-implanted layer is introduced as an intermediary between the piezoelectric film and supporting substrate. This intermediate layer has disturbed crystallinity that absorbs or scatters incident acoustic signals, preventing reflection and spurious noise while maintaining the thermal expansion suppression function of the bonded structure
Solution Approach 2:
The crystalline structure parameter of the supporting substrate surface is changed through ion implantation, creating a region with disturbed crystallinity. This parameter change transforms the interface from a reflective boundary to an absorbing/scattering region, eliminating spurious noise while preserving thermal characteristics
2Object-generated harmful factors
If the bonding surface is roughened to reduce reflection, then spurious noise is reduced, but bonding reliability decreases
Solution Approach 1:
The ion implantation is applied locally only to the bonding surface region of the supporting substrate, creating a localized layer with disturbed crystallinity. The bulk material and other surfaces maintain their original properties, ensuring that bonding reliability is preserved while spurious noise is reduced at the interface
3Ease of manufacture
If an adhesive is used to bond the piezoelectric material, then bonding is achieved, but device reliability is compromised
Solution Approach 1:
The chemical bonding mechanism of adhesives is replaced with a physical/structural solution: ion implantation creates a crystallinity-disturbed layer that provides acoustic signal absorption. This substitution eliminates the need for adhesives while maintaining bonding integrity and improving reliability through direct material bonding
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
This approach effectively reduces spurious noise and improves temperature stability by absorbing or scattering incident signals at the interface, leading to improved performance and reliability of surface acoustic wave devices.
Implementation Method 1
an ion implanting step of implanting ions from a bonding surface of the supporting wafer, to disturb crystallinity near the bonding surface is executed
Implementation Method 2
a signal incident from the stacking wafer which is a piezoelectric material is absorbed or scattered near an interface between the stacking wafer and the supporting wafer
Implementation Method 3
Lithium tantalate (LT) and lithium niobate (LN) that are general piezoelectric materials are widely used as materials of surface acoustic wave (SAW) devices
Implementation Method 4
lithium tantalate and lithium niobate have very high coefficients of thermal expansion
Data Source
Figure 1(a)~1(c)
Figure 2
Figure 3~4
AI summary
To provide a method for producing a composite wafer capable of reducing a spurious arising by reflection of an incident signal on a joint interface between a lithium tantalate film and a supporting substrate, in the composite wafer including a supporting substrate having a low coefficient of thermal expansion, and a lithium tantalate film having a high coefficient of thermal expansion stacked on the supporting substrate. The method for producing a composite wafer is a method for producing a composite wafer that produces a composite wafer by bonding a lithium tantalate wafer having a high coefficient of thermal expansion to a supporting wafer having a low coefficient of thermal expansion, wherein prior to bonding together, ions are implanted from a bonding surface of the lithium tantalate wafer and/or the supporting wafer, to disturb crystallinity near the respective bonding surfaces.