Conductive Stabilization Posts for On-Wafer Micro LED Testing
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Solution Overview
Problem
Display panels fabricated using micro LED transfer techniques are prone to defects due to issues in the transfer and integration processes, which can result in non-functional micro LEDs on the receiving substrate.
Innovation Solution
The development of conductive stabilization structures on a donor substrate that support and retain micro LEDs, allowing for electrical testing before transfer, comprising a carrier substrate with a stabilization layer of non-metallic matrix pillars and a metallic liner layer for mechanical and electrical connection, enabling verification of LED operability before integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If micro LEDs are transferred from donor substrate to receiving substrate using electrostatic transfer heads, then the micro LEDs can be integrated into display panels, but defects occur due to issues in transfer and integration processes resulting in non-functional micro LEDs
Solution Approach 1:
The patent implements preliminary electrical testing of micro LEDs on the donor substrate before the transfer process. Test pads are formed on the donor substrate and electrically connected to the micro LEDs through the stabilization posts, allowing functionality verification to occur in advance. This preliminary action identifies defective LEDs before they are transferred, ensuring only functional LEDs are moved to the receiving substrate, thus resolving the contradiction between transfer efficiency and reliability.
2Measurement precision
If micro LEDs are tested after transfer to receiving substrate, then functionality can be verified, but defective LEDs cannot be recovered and require rework
Solution Approach 1:
The patent performs functionality verification as a preliminary action on the donor substrate before transfer. The test pads are electrically connected to micro LEDs while they remain on the donor substrate, enabling testing before the irreversible transfer process. This allows defective LEDs to be identified and left on the donor substrate, eliminating the need for complex rework operations on the receiving substrate and significantly improving ease of repair.
Solution Approach 2:
The patent extracts the testing function from the post-transfer process and relocates it to the pre-transfer stage on the donor substrate. By separating the testing operation from the final integrated structure, the system enables easy identification and exclusion of defective LEDs without affecting the receiving substrate or requiring complex repair operations, thus resolving the contradiction between measurement precision and ease of repair.
3Device complexity
If all micro LEDs are transferred without pre-testing, then transfer process is simpler and faster, but defect rate increases on the receiving substrate
Solution Approach 1:
The patent incorporates preliminary electrical testing through test pads and stabilization posts as an integrated part of the donor substrate structure. This preliminary action adds minimal complexity to the transfer process while dramatically improving display panel quality by ensuring only functional LEDs are transferred. The testing infrastructure is built into the donor substrate fabrication process, so the additional complexity is absorbed during manufacturing rather than during transfer operations.
Solution Approach 2:
The patent introduces test pads as an intermediary element between the micro LEDs and the external testing equipment. These test pads are formed on the donor substrate and provide electrical connection points for testing micro LED functionality before transfer. This intermediary structure enables quality verification without complicating the transfer process itself, as the testing occurs on the donor substrate using the stabilization posts as conductive pathways, thus resolving the contradiction between device complexity and reliability.
4Reliability
If test pads are formed on donor substrate and electrically connected to stabilization posts, then pre-transfer testing is enabled, but additional manufacturing steps are required
Solution Approach 1:
The patent merges the test pad formation and electrical connection to stabilization posts with the existing donor substrate fabrication process. The test pads are formed using standard semiconductor manufacturing techniques that are integrated into the workflow for creating the donor substrate with micro LEDs and stabilization posts. By combining these testing infrastructure elements with the existing manufacturing process rather than adding separate discrete steps, the patent enables LED operability verification while minimizing the impact on ease of manufacture.
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 ensures the transfer of 'known good' micro LEDs to the receiving substrate, reducing defects by allowing for pre-transfer testing and validation of LED functionality, thereby improving the reliability of micro LED displays.
Implementation Method 1
a stabilization layer including a plurality of pillars formed of a non-metallic matrix material including an organic-based or inorganic-based backbone. A metallic liner layer is over the plurality of pillars, where the metallic liner layer and the plurality of pillars form a plurality of stabilization posts
Implementation Method 2
it has been proposed in U.S. Pat. No. 8,835,940 to stage an array of micro LEDs on an array of stabilization posts formed of an adhesive bonding material, such as a thermoset material. During the transfer process, it is described that the array of electrostatic transfer heads generate a sufficient pressure to overcome the adhesion strength between the adhesive bonding material and the micro LEDs
Data Source
AI summary
LED donor substrates and conductive architectures for on-wafer testing are described. In an embodiment, an array of LEDs is supported by an array of electrically conductive stabilization posts. The electrically conductive stabilization posts can be coupled with a test pad for on-wafer testing prior to transferring the LEDs to a receiving substrate.