OLED Bank Pattern Design for Ink-Jet Thickness Uniformity
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Solution Overview
Problem
The ink-jet printing process for forming organic emission layers in OLED devices faces challenges due to the difficulty in securing enough nozzles opposite to a single sub-pixel, leading to thickness deviations, which are exacerbated in high-definition displays where fewer nozzles are required, making the process sensitive to nozzle abnormalities.
Innovation Solution
The formation of additional bank patterns with openings that expose parts of the driving domain within sub-pixel regions allows for a wider occupation area of the organic emission layer, increasing the number of nozzles opposite to each sub-pixel and minimizing thickness deviations even if one nozzle shows abnormality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the ink-jet printing process uses a limited number of nozzles to form the organic emission layer in high-definition OLED devices, then the device complexity is reduced, but the manufacturing precision deteriorates due to thickness deviations
Solution Approach 1:
The patent introduces a third dimension by forming a bank pattern with a stepped structure having different height levels. The first bank pattern defines the emission region boundary, while the second bank pattern is formed at a higher level to create an opening that exposes both the emission region and part of the driving region. This vertical dimensionality allows the organic emission layer to be deposited over a wider area through the same number of nozzles, improving thickness uniformity without increasing device complexity
Solution Approach 2:
The bank pattern is segmented into two distinct levels: the first bank pattern forming the base structure that defines the emission region boundary, and the second bank pattern forming an elevated structure with an opening. This segmentation creates multiple deposition zones that can be selectively targeted by the ink-jet nozzles, allowing better distribution of the organic emission layer material and reducing thickness deviations
2Productivity
If the number of nozzles is reduced for high-definition displays, then the productivity is improved by simplifying the manufacturing process, but the reliability deteriorates due to sensitivity to nozzle abnormalities
Solution Approach 1:
The bank pattern structure is designed beforehand to create a widened occupation area for the organic emission layer. This pre-structured approach provides a buffer that compensates for potential nozzle abnormalities during the deposition process. The stepped configuration with the opening ensures that even if one nozzle fails or deposits unevenly, the overall thickness uniformity is maintained through the distributed deposition area
Solution Approach 2:
By adding the vertical dimension through the stepped bank pattern, the patent creates additional deposition pathways and areas. The opening in the second bank pattern exposes both the emission region and part of the driving region, allowing the organic emission layer to be formed over a broader area with the same number of nozzles, thereby reducing sensitivity to individual nozzle performance variations
Data Source
AI summary
An organic light emitting display (OLED) device is disclosed. The OLED device includes a substrate configured to include a sub-pixel defined into an emission region and a driving region. A first bank pattern configured to define the emission region of the sub-pixel is formed on the substrate. A second bank pattern configured to include an opening, which exposes the emission region and a part of the driving region, is formed on a part of an upper surface of the first bank pattern. An organic emission layer is formed in the opening. As such, the occupied area of the organic emission layer becomes wider. Therefore, the thickness deviation of the organic emission layer is prevented or minimized.