OLED Cathode Contact Holes for Uniform Current Distribution

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Solution Overview

Problem

In organic electro luminescence displays, the use of a single large contact hole for connecting the cathode power line to the cathode electrode leads to uneven current distribution, resulting in a voltage drop and inconsistent brightness due to high resistance in transparent conductive materials.

Innovation Solution

The implementation of multiple contact holes arranged in a matrix or column configuration between the cathode power line and the cathode electrode, with their total circumference exceeding the overlapped region, enhances current mobility and prevents voltage drops by distributing current density more evenly.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If a single large contact hole is used to connect the cathode power line to the cathode electrode, then the connection area is sufficient, but the current density becomes concentrated at the edge of the contact hole, causing voltage drop and inconsistent brightness

Engineering Contradiction:

Improvecontact hole areaVSAvoidcurrent distribution uniformity

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The single large contact hole is divided into multiple smaller contact holes arranged in an array. This segmentation distributes the current flow across multiple pathways, preventing current concentration at the edges of a single large hole and thereby eliminating the voltage drop and brightness inconsistency issues.

Inventive Principle:

Principle #1Segmentation

2Illumination intensity

If transparent conductive material is used for the cathode electrode, then the display achieves top-emission with high aperture ratio, but the high resistance value causes voltage drop and inconsistent brightness

Engineering Contradiction:

Improveaperture ratioVSAvoidbrightness consistency

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The contact hole structure is segmented into multiple smaller holes, which distributes the current flow and reduces the effective resistance of the cathode electrode. This allows the use of transparent conductive material while maintaining brightness consistency across the display.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The cathode power line is positioned to overlap with the cathode electrode in a specific region, creating a localized high-conductivity path. This local quality enhancement ensures uniform voltage distribution across the transparent cathode electrode while maintaining the overall transparency and aperture ratio.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If the cathode power line overlaps the cathode electrode, then direct connection is achieved, but current concentration at the contact hole edge causes voltage drop

Engineering Contradiction:

Improveconnection simplicityVSAvoidcurrent mobility

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The overlapping region between the cathode power line and cathode electrode is connected through multiple segmented contact holes rather than a single continuous connection. This segmentation improves current mobility by distributing the current flow across multiple pathways while maintaining manufacturing simplicity.

Inventive Principle:

Principle #1Segmentation

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 configuration increases current mobility and maintains consistent brightness by reducing voltage drops, thereby improving the overall performance of the organic electro luminescence display.

Implementation Method 1

organic electro luminescence display

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 2

transparent conductive material has a high resistance value, however, which causes a voltage (IR) drop

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS7453203B2Organic electro luminescence display including an insulating layer having contact holes in a region where a power line overlaps an electrode

Publication Date: 2008.11.18 SAMSUNG DISPLAY CO LTD

AI summary

An organic electro luminescence display comprises a pixel portion on which a plurality of pixels are arranged with a first electrode, a second electrode, and an organic thin film layer interposed between the first and second electrodes, a first power line supplying a first level voltage to the pixels of the pixel portion; and a second power line having at least a region overlapped with the second electrode to supply a second level voltage to the second electrode, and an insulating layer having a plurality of contact holes in the overlapped region between the second power line and the second electrode. The sum of the circumferences of each contact hole is greater than the circumference of the overlapped region.