OLED Upper Electrode Bus Line Connection via Laser Ablation
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Solution Overview
Problem
Active matrix OLED displays face challenges with low aperture ratio due to opaque circuitry and high sheet resistance of transparent upper electrodes, leading to voltage drops, increased power consumption, and reduced luminance uniformity.
Innovation Solution
A method involving a substrate with a conductive bus line and a radiation absorbing structure, where radiation is used to ablate the organic electroluminescent media, creating an opening for forming an electrical connection between the upper electrode and the bus line, thereby reducing resistance and improving conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent upper electrode is used in bottom-emitting OLED configuration, then light emission is enabled, but sheet resistance is high causing voltage drops and reduced luminance uniformity
Solution Approach 1:
The upper electrode is segmented into pixel electrode regions and bus line regions. The bus line regions are made opaque and highly conductive, while pixel electrodes remain transparent. This segmentation allows different regions to serve different functions: transparent pixel electrodes for light emission and opaque bus lines for low-resistance current distribution.
Solution Approach 2:
Different regions of the upper electrode are given different optical and electrical properties. Pixel electrode areas are transparent with moderate conductivity for light emission, while bus line areas are opaque with high conductivity for efficient current transport. This local differentiation resolves the contradiction between transparency and conductivity requirements.
2Ease of operation
If opaque circuitry is present in bottom-emitting OLED, then active matrix driving is enabled, but aperture ratio is reduced
Solution Approach 1:
The circuitry is moved from the substrate plane to the upper electrode plane. By forming bus lines and circuit elements in the upper electrode layer rather than on the substrate, the circuitry occupies space above the pixel area rather than blocking light from the substrate side, thereby maintaining high aperture ratio while enabling active matrix driving.
3Reliability
If radiation absorbing structure is added to form openings in organic EL media, then electrical connection is improved, but device complexity increases
Solution Approach 1:
The radiation absorbing structure is merged with the upper electrode formation process. The same opaque material that forms the bus lines also serves as the radiation absorbing structure for creating openings in the organic EL media. This merging eliminates separate fabrication steps and reduces overall device complexity while maintaining reliable electrical connections.
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 enhances the conductivity of the upper electrode, increases aperture ratio, and simplifies the fabrication process by reducing the need for precise patterning and alignment, leading to improved brightness uniformity and extended device lifespan.
Implementation Method 1
exposing the radiation absorbing structure to radiation to produce heat sufficient to ablate a portion of the organic EL media
Implementation Method 2
exposing the radiation absorbing structure to radiation to produce heat sufficient to ablate a portion of the organic EL media thereby forming an opening
Data Source
AI summary
A method of making an OLED device, including providing a substrate having a first electrode and a conductive bus line provided over the substrate and organic EL media provided over the first electrode and over the conductive bus line; forming a radiation absorbing structure associated with the conductive bus line; exposing the radiation absorbing structure to radiation to produce heat sufficient to ablate a portion of the organic EL media thereby forming an opening in the organic EL media; and forming a second electrode over the organic EL media, and through the opening in the organic EL media thereby forming an electrical connection between the second electrode to the conductive bus line.