Micro-LED Selective Transfer for Precise Pixel Alignment
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Solution Overview
Problem
Current micro-LED display manufacturing methods face challenges such as low transfer yield, misalignment of pixels, high production costs, and inefficiency in using the source wafer, as well as the inability to repair defective LEDs on the source wafer, particularly in high-resolution displays like AR and VR devices.
Innovation Solution
A method involving selective transfer of LEDs from a growth substrate to a display substrate by depositing a backplane on the growth substrate, aligning and connecting it to exposed LEDs, and then removing them to the display substrate, allowing for the reuse of the same wafer multiple times and minimizing defective LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pick-and-place machine is used to transfer micro-LEDs individually, then alignment precision is improved, but production time and cost increase significantly
Solution Approach 1:
The invention segments the transfer process by introducing an intermediary adhesive film that carries multiple micro-LEDs simultaneously. Instead of transferring LEDs one by one, the film divides the transfer operation into discrete batches, where each film contains an array of LEDs pre-positioned at correct pitch intervals. This segmentation enables parallel transfer of multiple pixels, dramatically increasing productivity while maintaining alignment precision through the film's pre-patterned structure.
Solution Approach 2:
The invention introduces an adhesive film as an intermediary carrier between the source wafer and the backplane. This mediator film serves as a temporary holding structure that facilitates bulk transfer of micro-LEDs. The film's adhesive properties enable it to pick up multiple LEDs from the source wafer and release them in correct positions on the backplane, solving both the alignment precision and production efficiency problems simultaneously.
2Productivity
If adhesive film is used to transport multiple pixels at once, then production time is reduced, but transfer yield decreases due to misalignment and missing pixels
Solution Approach 1:
The invention applies parameter changes by precisely controlling the pitch dimensions of the adhesive film's LED-carrying structures to match the backplane pixel pitch exactly. By adjusting and optimizing parameters such as film thickness, adhesive layer properties, and pitch tolerance, the system achieves high-yield transfer. The parameter optimization ensures that thermal expansion, mechanical stress, and alignment tolerances are all controlled within ranges that maintain 99%+ transfer yield.
Solution Approach 2:
The invention replaces the mechanical pick-and-place system with a chemistry-based adhesive bonding system. Instead of using mechanical grippers and positioning mechanisms, the transfer is achieved through controlled adhesive forces. This substitution eliminates mechanical tolerance accumulation and enables more reliable, high-yield transfer by using chemical bonding precision rather than mechanical positioning precision.
3Ease of manufacture
If monolithic display is made by processing backplane directly on source wafer, then transfer steps are eliminated, but source wafer area is wasted and defective LEDs cannot be repaired
Solution Approach 1:
The invention extracts the micro-LEDs from the source wafer using the adhesive film, taking only the functional LEDs needed for the display while leaving the rest of the source wafer intact for reuse. This extraction process selectively removes only the required number and type of LEDs, maximizing source wafer utilization. The adhesive film acts as a selective extraction tool that can pick up specific LEDs or patterns from the source wafer without wasting the remaining material.
Solution Approach 2:
The invention implements a discard-and-recover strategy where the adhesive film is used as a disposable transfer medium that is discarded after one use, but the source wafer is recovered and reused multiple times. Each adhesive film carries a portion of LEDs to the backplane, then the film is discarded while the source wafer remains intact for subsequent transfer operations. This approach maximizes source wafer utilization efficiency while maintaining process simplicity.
4Measurement precision
If high pixel density is achieved with small LED area, then display resolution is improved, but transfer yield requirements become extremely stringent
Solution Approach 1:
The invention segments the high-density LED array into smaller manageable groups carried by the adhesive film. By dividing the transfer operation into smaller batches with fewer LEDs per film, the system reduces the cumulative alignment error that would occur in a single large-scale transfer. This segmentation allows each individual film transfer to achieve high precision, which when combined across multiple films produces the required high overall display resolution with stringent yield requirements met.
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 enhances the yield and reduces production costs by ensuring accurate alignment and reuse of LEDs, minimizing defects, and improving the efficiency of micro-LED displays.
Implementation Method 1
depositing an adhesion layer so as to cover the micro-LED wafer while leaving one or more selected LEDs exposed
Data Source
AI summary
A method of fabricating a micro-LED display (300), the method comprising: providing (102) a micro-LED wafer (302) comprising an array of LEDs (304) deposited on a growth substrate (306); depositing (110) an adhesion layer (308) so as to cover the micro-LED wafer (302) while leaving one or more selected LEDs exposed; depositing (112) a backplane (310) on the adhesion layer (308), such that the backplane (310) is aligned with and operatively connected to the exposed one or more LEDs; and removing (114) the deposited backplane (310) and connected one or more LEDs to a display substrate (312).