Top-emissive OLED Auxiliary Cathode Under-cut Structure
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Solution Overview
Problem
In large-area organic light-emitting diode displays, cathodes made of transparent conductive materials like indium tin oxide or indium zinc oxide exhibit high surface resistance, leading to uneven voltage distribution and brightness across the display, which affects image quality.
Innovation Solution
The implementation of an auxiliary cathode with an under-cut structure that directly connects to the cathode, reducing surface resistance and simplifying the manufacturing process by eliminating the need for additional mask processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a transparent conductive material is used for the cathode to enable top-emissive display, then the display structure is achieved, but the surface resistance increases leading to uneven voltage distribution
Solution Approach 1:
The cathode system is segmented into two parts: a transparent conductive cathode layer and a separate auxiliary cathode with low resistance. The auxiliary cathode is positioned at the periphery and electrically connected to the transparent cathode through contact holes, creating a segmented structure that combines the advantages of both transparent materials and low-resistance metals.
Solution Approach 2:
The auxiliary cathode acts as an intermediary element that mediates between the power supply and the transparent cathode. It provides a low-resistance electrical path that compensates for the high surface resistance of the transparent conductive material, ensuring uniform voltage distribution across the display area.
2Reliability
If an auxiliary cathode is added to reduce surface resistance, then voltage distribution improves, but device complexity increases
Solution Approach 1:
The auxiliary cathode is merged with the existing peripheral structures of the display device. It is integrated into the same layer as the light shielding layer and uses the same manufacturing processes, combining multiple functions into a single structural element without requiring separate dedicated space or additional process steps.
Solution Approach 2:
The auxiliary cathode serves multiple functions simultaneously: it acts as a low-resistance electrical connection, provides a reference potential for the transparent cathode, and can serve as part of the light shielding structure. This multi-functionality reduces the need for separate components and simplifies the overall device architecture.
3Manufacturing precision
If additional mask processes are used to create auxiliary cathode connections, then connection precision improves, but manufacturing time increases
Solution Approach 1:
The auxiliary cathode and its connection structures are formed during the preliminary stages of manufacturing, specifically during the same process steps used to create the light shielding layer and other peripheral structures. The contact holes are formed early in the process sequence, allowing subsequent layers to be deposited without requiring additional alignment or masking operations.
Solution Approach 2:
The manufacturing process is designed so that the formation of the auxiliary cathode and its connections is achieved through self-aligned processes. The peripheral structures automatically define the positions of contact holes and connections, eliminating the need for separate mask alignment operations and reducing manufacturing complexity.
Data Source
AI summary
A top-emissive organic light-emitting diode display includes a substrate, an auxiliary line, an insulating film, an auxiliary cathode, a passivation film, a planarization film, an under-cut opening, an under-area, a connecting terminal, an organic emission layer, and a cathode. An under-cut opening exposes one end of the auxiliary cathode. The under-area is formed inside the under-cut opening by removing the insulating film underlying the exposed end of the auxiliary cathode. The connecting terminal on the planarization film extends to the under-cut opening and makes contact with the exposed auxiliary cathode. The organic emission layer is stacked on the surface of the auxiliary cathode, and is not applied to the under-area and exposes the side of the connecting terminal making contact with the auxiliary cathode. The cathode is stacked on the organic emission layer and makes contact with the side of the connecting terminal not covered by the organic emission layer.