Color Filter Placement to Prevent LCD Sub-Pixel Shorting
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Solution Overview
Problem
In liquid crystal displays (LCDs) with a color filter on array (COA) structure, the formation of color filters on the lower substrate leads to short circuits between sub-pixels due to residual conductive layers at the boundary between regions with and without color filters, caused by the thickness differences in photoresist during the manufacturing process.
Innovation Solution
The color filter is designed to remain in the boundary portion between sub-pixels on the storage electrode, ensuring that the conductive layer for forming pixel electrodes is not left behind, thereby preventing short circuits. This is achieved by forming a color filter that is thicker than the photoresist and carefully removing it where pixel electrodes are formed, ensuring proper exposure and development.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the color filter is formed to be thicker than the photoresist to ensure proper coverage, then the color filter can be completely removed in the photoresist developing process, but the photoresist cannot be properly exposed at the boundary region where the color filter is formed, leading to incomplete removal and short circuits between sub-pixels
Solution Approach 1:
The color filter formation process is segmented into two distinct stages: first forming the color filter pattern, then forming the pixel electrode pattern. This segmentation allows the color filter to remain during photoresist formation, serving as a mask that prevents short circuits while enabling proper photoresist exposure through the transparent regions.
Solution Approach 2:
The color filter is formed in advance before the pixel electrode pattern is created. This preliminary action ensures that the color filter is already in place to prevent conductive layer residue at boundaries before the photoresist exposure process begins, thereby preventing short circuits from occurring.
2Ease of manufacture
If the color filter is formed to be about two or more times thicker than the usual photoresist, then the color filter can serve as an effective mask, but the photoresist thickness becomes insufficient for proper exposure and development at the boundary regions
Solution Approach 1:
Instead of making the photoresist thicker to ensure proper exposure, the approach is inverted: the color filter is maintained at its standard thick formulation to serve as the primary masking layer, while the photoresist is applied at normal thickness. The color filter's transparency in certain regions allows proper light exposure to reach the photoresist, solving the exposure problem without compromising masking effectiveness.
3Device complexity
If the color filter remains on the storage electrode to prevent short circuits, then the manufacturing process is simplified, but the structural complexity of the storage capacitor region increases due to the presence of color filter material
Solution Approach 1:
The color filter is selectively positioned only where needed - specifically on the storage electrode region where it serves to prevent short circuits. In other regions where pixel electrodes are formed, the color filter is removed. This local quality approach maintains manufacturing simplicity while minimizing structural complexity to only where it provides functional benefit.
Data Source
AI summary
A liquid crystal display (LCD) and a method of manufacturing the same in which the color filter remains in a boundary portion between pixel electrodes on a storage electrode line or the pixel and common electrodes to prevent residuals of the pixel electrode from shorting the pixel electrodes when the color filter is removed.