Micro LED Transfer via Phase Change Bonding Layer
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Solution Overview
Problem
Current methods for forming and transferring micro light emitting diodes (LEDs) based on gallium nitride (GaN) face challenges in integrating these devices onto various substrates while maintaining their structural and electrical integrity, particularly due to lattice mismatch and thermal expansion differences between GaN and common substrates like sapphire or silicon.
Innovation Solution
A method involving the formation of a micro LED structure with a reflective metallization stack, an electrically insulating spacer, and a bonding layer with a low liquidus temperature, allowing for the transfer of micro LEDs from a growth substrate to a receiving substrate using a transfer head that induces a phase change in the bonding layer to pick up and place the micro LEDs, ensuring strong adhesion and structural integrity during the transfer process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If micro LEDs are transferred from GaN growth substrate to foreign substrates like sapphire or silicon, then the structural and electrical integrity is compromised due to lattice mismatch and thermal expansion differences, but transferring to different substrates is necessary for diverse applications
Solution Approach 1:
The patent introduces a bonding layer as an intermediary between the GaN micro LED structure and the foreign substrate. This bonding layer serves as a mediator that accommodates the lattice mismatch and thermal expansion differences, allowing transfer to diverse substrates (sapphire, silicon, glass, plastic) while maintaining the structural and electrical integrity of the micro LEDs. The bonding layer absorbs the mechanical stress and thermal mismatch that would otherwise damage the micro LEDs during transfer and operation.
2Strength
If permanent bonding layer is used to bond micro LEDs to acceptor substrate, then strong adhesion is achieved, but the bonding process requires high temperature processing that may damage the micro LED structure
Solution Approach 1:
The patent utilizes phase transition of the bonding layer material to achieve bonding at lower temperatures. The bonding layer is designed to undergo phase change (melting/freezing or solid-state phase transformation) at temperatures compatible with micro LED structures, enabling strong adhesion without exposing the micro LEDs to damaging high temperatures. This allows permanent bonding while protecting the sensitive GaN micro LED structure from thermal degradation.
3Ease of manufacture
If micro LEDs are diced from wafer to form individual chips, then individual device fabrication is achieved, but the dicing process may damage the delicate micro LED structure and reduce yield
Solution Approach 1:
The patent performs preliminary actions to prepare the micro LED structures for safe dicing. The bonding layer is formed and partially processed before dicing, providing mechanical support and stress distribution that protects the delicate micro LED structures during the subsequent dicing operation. This preliminary preparation ensures that individual chips can be fabricated with minimal damage and high yield.
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 enables the efficient transfer and integration of micro LEDs onto diverse substrates, such as display or lighting substrates, with high transfer rates and maintains the electrical and structural integrity of the micro LEDs, facilitating their use in heterogeneous integrated systems.
Implementation Method 1
heating the bonding layer above a liquidus temperature of the bonding layer
Implementation Method 2
create a phase change in the bonding layer
Data Source
AI summary
A method of fabricating and transferring a micro device and an array of micro devices to a receiving substrate are described. In an embodiment, an electrically insulating layer is utilized as an etch stop layer during etching of a p-n diode layer to form a plurality of micro p-n diodes. In an embodiment, an electrically conductive intermediate bonding layer is utilized during the formation and transfer of the micro devices to the receiving substrate.