Micro Epitaxial LED Transfer via Matched Thermal Expansion Substrates
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Solution Overview
Problem
The current manufacturing process of light emitting diodes (LEDs) faces challenges with alignment precision due to thermal stress caused by differences in thermal expansion coefficients between growth substrates and permanent or temporary substrates during the transfer process.
Innovation Solution
A light emitting device is designed with micro epitaxial structures on a first substrate, bonded to a second substrate using a thermocompression bonding method, where the thermal expansion coefficients of both substrates are matched within a specific ratio, ensuring precise alignment and minimizing displacement during transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a sapphire substrate is used as the growth substrate, then the epitaxial structure can be formed, but the alignment precision deteriorates due to thermal stress from coefficient of thermal expansion mismatch
Solution Approach 1:
The patent divides the substrate system into three distinct layers: a sapphire growth substrate, a temporary substrate with matched thermal expansion coefficient, and the final permanent substrate. This segmentation allows the epitaxial structure to be transferred through an intermediate medium that compensates for thermal stress, resolving the alignment precision issue caused by direct bonding between sapphire and permanent substrate
Solution Approach 2:
The patent introduces a temporary substrate as an intermediary layer between the sapphire growth substrate and the permanent substrate. This temporary substrate has a coefficient of thermal expansion matched to the sapphire, serving as a mediator that absorbs and compensates for thermal stress during the transfer process, thereby maintaining alignment precision
2Manufacturing precision
If the coefficient of thermal expansion of substrates is matched, then displacement is minimized, but substrate material selection becomes more constrained
Solution Approach 1:
The substrate system is segmented into multiple functional layers with different material properties. The sapphire growth substrate maintains its advantages for epitaxial growth, while the temporary substrate provides thermal expansion matching, and the permanent substrate offers final device integration. This segmentation allows each layer to be optimized independently for its specific function
Solution Approach 2:
The temporary substrate acts as an intermediary that decouples the material selection constraints. It provides the necessary thermal expansion matching property without requiring the permanent substrate to have matched thermal properties, thereby expanding material selection flexibility while maintaining precision
3Ease of manufacture
If micro epitaxial structures are transferred from growth substrate, then device integration is enabled, but thermal stress causes shift phenomenon affecting alignment
Solution Approach 1:
The patent performs preliminary bonding of the epitaxial structure to a temporary substrate with matched thermal expansion coefficient before final transfer to the permanent substrate. This preliminary action on a thermally compatible medium prevents thermal stress-induced shifting during the critical transfer operation, enabling subsequent precise device integration
Solution Approach 2:
The temporary substrate serves as an intermediary transfer medium that enables device integration while preventing alignment errors. It facilitates the transfer process by providing thermal compatibility, allowing the epitaxial structures to be moved and integrated without experiencing the harmful thermal stress that would cause shifting
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 allows for the transfer of micro epitaxial structures with fixed pitch, enhancing alignment precision and preventing displacement, thereby improving the manufacturing yield and reliability of the light emitting device.
Implementation Method 1
The micro epitaxial structures are disposed on the first substrate and bonded with the second substrate via a thermocompression bonding method
Implementation Method 2
The first adhesive layer is disposed between the micro epitaxial structures and the second substrate. The second adhesive layer is disposed between the micro epitaxial structures and the first substrate
Data Source
AI summary
A light emitting device includes a first substrate, a second substrate and a plurality of micro epitaxial structures. The second substrate is disposed opposite to the first substrate. The micro epitaxial structures are periodically disposed on the substrate and located between the first substrate and the second substrate. A coefficient of thermal expansion of the first substrate is CTE1, a coefficient of thermal expansion of the second substrate is CTE2, a side length of each of the micro epitaxial structures is W, W is in the range between 1 micrometer and 100 micrometers, and a pitch of any two adjacent micro epitaxial structures is P, wherein W/P=0.1 to 0.95, and CTE2/CTE1=0.8 to 1.2.