Liquid Crystal Display Alignment Film Thickness Control
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Solution Overview
Problem
In liquid crystal display devices, the lateral displacement of columnar spacers due to temperature cycles or external pressure causes the alignment film to be scraped off, leading to the generation of light spots that degrade image quality.
Innovation Solution
A liquid crystal display device is designed with a concavo-convex pedestal on the TFT substrate, where the convex portion has a lower height than the concave portion, and the top end of the columnar spacer contacts multiple convex portions, reducing the alignment film thickness on the convex portion and preventing scraping by the columnar spacer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If columnar spacers are used to control liquid crystal layer thickness, then gap control precision is improved, but alignment film scraping occurs due to lateral displacement under temperature cycles or external pressure
Solution Approach 1:
The pedestal structure is designed with non-uniform thickness, creating a concave portion with greater thickness than the convex portion. This local variation in thickness provides a cushioning effect specifically at the concave portion where the alignment film is most vulnerable to scraping, while maintaining the overall spacer function. The local quality change allows the alignment film to be protected without compromising the columnar spacer's gap control capability.
Solution Approach 2:
The concave portion of the pedestal is designed in advance with greater thickness to serve as a cushioning structure before any lateral displacement of the columnar spacer occurs. This pre-designed cushioning absorbs the impact when the columnar spacer shifts laterally under temperature cycles or external pressure, preventing the alignment film from being scraped off and eliminating light spots before they can form.
2Manufacturing precision
If alignment film is formed on the entire pedestal surface, then initial alignment is improved, but scraping occurs when columnar spacer displaces laterally
Solution Approach 1:
The pedestal is designed with spatially varying thickness, creating a concave portion with greater thickness than the convex portion. This local variation allows the alignment film to be thicker at the concave portion (providing better initial alignment) while being thinner or absent at the convex portion (preventing scraping when the columnar spacer displaces laterally).
Solution Approach 2:
Instead of making the alignment film uniformly thick across the entire pedestal (which would maximize initial alignment but cause scraping), the invention inverts the approach by creating a thickness gradient where the concave portion has greater thickness than the convex portion. This inversion allows the alignment film to be protected at critical locations while maintaining sufficient thickness for initial alignment.
3Ease of manufacture
If uniform thickness alignment film is used on the pedestal, then manufacturing simplicity is maintained, but light spots are generated due to scraping
Solution Approach 1:
The pedestal structure is designed with a concave portion that has greater thickness than the convex portion. This local variation in thickness is achieved through standard deposition techniques by controlling the deposition process to create the desired concave-convex profile. The result is that the alignment film naturally has greater thickness at the concave portion, providing protection against scraping while maintaining manufacturing feasibility through conventional processes.
Data Source
AI summary
A display device includes a first substrate, a second substrate and liquid crystals therebetween, the first substrate having a flat portion, an alignment film, and a concavo-convex pedestal formed in a pixel region, wherein the concavo-convex pedestal having at least two convex portions and recessed portions, and the at least two convex portions of the concavo-convex pedestal are at a position lower than a position of the flat portion. A thickness of the alignment film on the convex portions is less than a thickness of the alignment film on the recessed portions, and a second substrate has a columnar spacer which contacts the at least two convex portions of the concavo-convex pedestal.