Micro-LED Transfer via Localized Joule Heating
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Solution Overview
Problem
Current micro-LED transfer methods involve heating all micro-LEDs during transfer, leading to performance degradation, reduced throughput, and increased thermal budgets, as well as complications in identifying and repairing defective LEDs, due to separate examination and transfer processes.
Innovation Solution
A micro-LED transfer method using a transfer head with pickup units that apply current selectively to heat only the bonding layers of targeted micro-LEDs, allowing for local heating, programmable transfer, and identification of good dies through I-V characteristics, enabling selective pickup and bonding onto a receiving substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If all micro-LEDs are heated up during transfer to melt bonding layers, then the micro-LEDs can be picked up and transferred, but the performance of the micro-LEDs degrades and thermal budget increases
Solution Approach 1:
The patent applies local heating by using a transfer head with heating elements that can selectively heat only the specific micro-LED location being transferred, rather than heating the entire substrate. This localized approach melts the bonding layer at the target position without subjecting all micro-LEDs to high temperature, thereby maintaining their performance while enabling transfer.
Solution Approach 2:
The transfer process is segmented into discrete steps where individual micro-LEDs or small groups are transferred sequentially rather than all at once. The transfer head moves across the substrate, heating and transferring micro-LEDs one at a time or in small batches, reducing the cumulative thermal exposure for each device.
2Productivity
If all micro-LEDs are heated up during transfer, then bonding layers are melted for transfer, but more thermal budgets are required for whole substrate
Solution Approach 1:
The heating is localized to only the area being actively transferred at any given moment. The transfer head contains heating elements that concentrate thermal energy on the specific bonding layer being melted, rather than heating the entire substrate. This dramatically reduces the total thermal budget required for the transfer process.
3Productivity
If examination process and transfer process are separate, then bad micro-LEDs may be picked up and transferred, but repair procedure becomes complicated
Solution Approach 1:
The patent combines the examination and transfer processes into a single integrated operation. The transfer head is equipped with both inspection capabilities (such as optical sensors or electrical testing) and transfer functionality. This allows for real-time identification of defective micro-LEDs during the transfer process, enabling selective transfer of only good devices and simplifying repair procedures by avoiding transfer of bad LEDs in the first place.
4Adaptability or versatility
If transfer head picks up micro-LEDs in multiple cycles, then three-color micro-LEDs can be transferred, but all micro-LEDs are heated up in each cycle even though only some are picked up
Solution Approach 1:
The transfer head applies heating locally only to the specific micro-LED position being worked on during each cycle. When transferring red, green, and blue micro-LEDs in separate cycles, only the target micro-LED at the current position is heated, not all micro-LEDs on the substrate. This maintains performance while enabling multi-color transfer capability.
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 reduces performance degradation, increases throughput, and simplifies the repair process by ensuring only good micro-LEDs are transferred and bonded, while minimizing thermal stress on other LEDs.
Implementation Method 1
applying current to the micro-LEDs via the pickup units to heat up bonding layers between the micro-LEDs and the carrier substrate to be melted
Data Source
AI summary
A micro-LED transfer method and manufacturing method. The micro-LED (303) transfer method comprises: bringing pickup units (305) of a transfer head in contact with micro-LEDs (303) on a carrier substrate (301), wherein the pickup units (305) are able to apply current to the micro-LEDs (303); applying current to the micro-LEDs (303) via the pickup units (305) to heat up bonding layers (302) between the micro-LEDs (303) and the carrier substrate (301) to be melted; picking up the micro-LEDs (303) from the carrier substrate (301) with the transfer head; bonding the micro-LEDs (303) onto a receiving substrate (307); and removing the transfer head from the micro-LEDs.