Micro-LED Cathode Layout to Prevent Step-Induced Cracks
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Solution Overview
Problem
In micro-LED display devices, stress concentration at the step generated during the connection of the cathode electrode to a low potential voltage leads to cracks, which is a limitation in the design of inorganic light-emitting display devices.
Innovation Solution
The design includes a second electrode with a first region on the light-emitting elements and a second region extending past the end of the first optical layer, which is in contact with the contact electrode, and a second optical layer surrounding the first optical layer, to distribute stress evenly and prevent crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cathode electrode is connected to a low potential voltage through a step structure, then the electrical connection is achieved, but stress concentration occurs at the step leading to cracks
Solution Approach 1:
The patent extends the second electrode in a horizontal direction beyond the light-emitting elements to contact the contact electrode, creating a planar transition structure. This dimensional extension eliminates vertical steps and distributes stress across a larger area, preventing crack formation while maintaining electrical connectivity.
Solution Approach 2:
The extended second electrode region acts as an intermediary structure between the vertical electrode and the contact electrode. This intermediate region provides a gradual transition zone that distributes mechanical stress, preventing the stress concentration that would occur at a sharp step interface.
2Device complexity
If a step structure is used for electrode connection, then the device structure is simplified, but stress concentration leads to crack formation
Solution Approach 1:
The solution maintains structural simplicity by using a planar extension in the horizontal dimension rather than introducing complex three-dimensional structures. The second electrode simply extends beyond the light-emitting elements to contact the contact electrode, avoiding the need for additional layers or complex geometries.
3Reliability
If the second electrode is extended past the light-emitting elements, then stress is distributed evenly preventing cracks, but the device area increases
Solution Approach 1:
The electrode extension is implemented locally only in the regions where contact with the contact electrode is required, rather than extending the entire electrode structure. This localized extension provides the necessary stress distribution and crack prevention while minimizing the overall area increase of the display device.
Data Source
AI summary
A display device includes a plurality of first electrodes and a contact electrode on a substrate; a plurality of light-emitting elements on the plurality of first electrodes; a first optical layer between the plurality of light-emitting elements; and a second electrode on the plurality of light-emitting elements, the second electrode including a first region that is on the plurality of light-emitting elements and a second region that extends past an end the first optical layer and is in contact with the contact electrode.