OLED Cathode Undercut Structure for Uniform Large-Area Luminance
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Solution Overview
Problem
Large area OLED displays using transparent conductive materials for cathodes face issues with increased sheet resistance, leading to non-uniform luminance across the screen due to high resistivity, which affects picture quality.
Innovation Solution
Incorporating an auxiliary cathode directly connected to the cathode through an undercut structure, utilizing a metal material with low resistivity to reduce sheet resistance and ensure uniform voltage distribution, while simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If transparent conductive material is used for cathode to secure transmissivity, then transmissivity is improved, but sheet resistance increases
Solution Approach 1:
The cathode is constructed as a composite structure combining transparent conductive material (ITO or IZO) with auxiliary cathodes made of metal materials having low resistivity. This composite approach allows the main cathode to maintain transmissivity while the auxiliary metal cathodes provide low-resistance pathways to reduce sheet resistance across large display areas.
2Area of stationary object
If large area OLED display is manufactured, then display area is increased, but luminance uniformity deteriorates due to high sheet resistance
Solution Approach 1:
The cathode system is segmented into a main transparent cathode and multiple auxiliary metal cathodes distributed across the display area. Each auxiliary cathode creates a local low-resistance zone, and collectively they ensure uniform voltage distribution across the entire large display area, preventing luminance non-uniformity.
Solution Approach 2:
The auxiliary cathodes are positioned at specific locations (corners and/or centers) of the display area, adding a spatial dimension to the cathode structure. This strategic positioning creates multiple voltage reference points that ensure uniform potential distribution across the large area, overcoming the limitations of a single cathode structure.
3Reliability
If auxiliary cathode is added to reduce sheet resistance, then sheet resistance is reduced, but device complexity increases
Solution Approach 1:
Instead of uniformly increasing cathode complexity across the entire display, auxiliary cathodes are strategically placed only at critical locations (corners and/or centers) where voltage uniformity is most needed. This localized approach reduces sheet resistance effectively while minimizing the increase in overall device complexity.
Solution Approach 2:
The formation of auxiliary cathodes is merged with existing manufacturing processes. The auxiliary cathodes are formed using the same thin-film deposition techniques as the main cathode, and the undercut structure is created during the same etching process, thereby reducing additional process steps despite the enhanced cathode functionality.
4Ease of manufacture
If undercut structure is used to connect auxiliary cathode, then manufacturing process is simplified, but structural complexity increases
Solution Approach 1:
The undercut structure utilizes the self-aligned nature of thin-film deposition and etching processes. The auxiliary cathode material is deposited to partially overlap the main cathode, and the subsequent etching process automatically creates the undercut connection structure without requiring additional alignment steps or complex masking, thereby simplifying manufacturing despite the enhanced structural functionality.
Data Source
AI summary
An organic light-emitting diode display includes an auxiliary connection line on a substrate; an auxiliary cathode on and connected to the auxiliary connection line; a passivation layer covering the auxiliary cathode; an overcoat layer on the passivation layer; a connection terminal connected to the auxiliary cathode on the overcoat layer; an undercut opening on the overcoat layer exposing a portion of the auxiliary cathode, an under area being in the undercut opening and under one side of the connection terminal; a bank having a size larger than the undercut opening and exposing the entire undercut opening; an organic emission layer on a region other than the under area in the undercut opening exposing the portion of the auxiliary cathode; and a cathode directly connected to the exposed portion of the auxiliary cathode on which the organic emission layer is not formed in the under area of the undercut opening.