Micro LED Pixel Transfer by Area Selection to Prevent Mura
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Solution Overview
Problem
The process of transferring ultra-small light emitting devices, such as mini LEDs and micro LEDs, is inefficient due to the presence of defective products and variations in electrical and optical characteristics across the wafer, leading to time-consuming individual transfer and potential mura in displayed images.
Innovation Solution
A method and apparatus that involves manufacturing wafers with unit pixels, cutting them on a temporary substrate, measuring electrical or optical characteristics, and transferring selected pixels based on these measurements to a carrier substrate in predetermined areas, using ultraviolet rays to separate and transport the pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If individual transfer of light emitting devices is performed using pick-and-place, then defective products can be removed, but process time becomes excessively long
Solution Approach 1:
The patent segments the transfer process into two stages: first, collective transfer of multiple light emitting devices in a matrix pattern to the carrier substrate; second, individual removal of defective devices. This segmentation allows the majority of good devices to be transferred efficiently in groups while still enabling defect removal, thus resolving the time vs. reliability contradiction.
Solution Approach 2:
The patent performs preliminary collective transfer of all light emitting devices (including defective ones) to the carrier substrate in a matrix arrangement before individual defect removal. This preliminary action transfers the bulk of devices efficiently in one operation, and subsequent defect removal only affects a small fraction, thereby significantly reducing total process time while maintaining reliability.
2Ease of manufacture
If light emitting devices are transferred while maintaining relative locational relationship on wafer, then transfer process is simplified, but mura occurs in displayed image due to luminance variations
Solution Approach 1:
The patent applies local quality by measuring electrical and optical characteristics of each light emitting device at its specific location on the wafer, then selectively removing defective devices from the matrix pattern on the carrier substrate. This allows the transfer process to maintain simplicity (global matrix transfer) while achieving luminance uniformity (local defect removal based on measured characteristics).
Solution Approach 2:
The patent implements feedback by measuring the electrical and optical characteristics of each light emitting device before transfer, using this measurement data to identify defective devices, and then removing only those specific defective devices from the transferred matrix pattern. This feedback loop ensures that simplicity of collective transfer does not compromise luminance uniformity, as defects are corrected based on actual measured data.
3Loss of time
If collective transfer of light emitting devices is performed, then process time is reduced, but defective products cannot be removed
Solution Approach 1:
The patent segments the transfer process into two distinct phases: Phase 1 performs collective transfer of all devices in a matrix pattern to the carrier substrate (achieving time efficiency); Phase 2 performs individual removal of defective devices based on pre-measured characteristics (achieving reliability). This two-stage segmentation resolves the contradiction by allowing both collective efficiency and individual defect removal.
Solution Approach 2:
The patent performs preliminary measurement and identification of defective devices before the collective transfer, then removes only those identified defective devices after transfer. This preliminary action enables the collective transfer to proceed without interruption, maintaining short process time, while the subsequent targeted defect removal ensures high reliability.
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 the time required for the transfer process and prevents mura in displayed images by ensuring only high-quality pixels are transferred and arranged uniformly, improving the efficiency and quality of the display manufacturing process.
Implementation Method 1
a light source unit irradiating ultraviolet rays to the unit pixels on the temporary substrate under the wafer stage
Data Source
AI summary
A transfer method of a light-emitting element for a display, according to one or more embodiments of the present disclosure, comprises: producing a wafer having unit pixels; cutting the wafer on a temporary substrate to unify the unit pixels; measuring electrical or optical characteristics of the unified unit pixels; and transferring, to a carrier substrate, the unit pixels selected according to the electrical or optical characteristics, wherein the selected unit pixels are transferred to the carrier substrate in predetermined area-units encompassing a plurality of unit pixels.