Liquid Crystal Display Contact Hole Geometry for Uniform Alignment
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Solution Overview
Problem
As liquid crystal display devices increase in resolution, the small area of pixels and reduced spacing between contact holes lead to a higher probability of alignment film repulsion, resulting in regions without alignment film, causing noticeable display unevenness as these uncoated areas link together.
Innovation Solution
The solution involves optimizing the design of contact holes by ensuring a sufficient space between them relative to the pixel pitch, with a specific ratio of contact hole diameter to pixel pitch, and a tapered angle of the sidewall, along with a minimum thickness of the alignment film to prevent the alignment film from being repelled and ensure uniform coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution is increased, then the image quality is improved, but the area of each pixel becomes smaller and the spacing between contact holes is reduced, causing the alignment film to be repelled and form regions without alignment film
Solution Approach 1:
The patent changes the geometric parameters of the contact hole, specifically setting the tapered angle of the sidewall to 53 degrees or less. This parameter modification allows the alignment film to properly cover the contact hole region even when the pixel area is reduced for high resolution displays, thereby preventing display unevenness while maintaining high screen resolution
Solution Approach 2:
The patent introduces a specific dimensional constraint by controlling the tapered angle of the contact hole sidewall. This angular parameter controls the three-dimensional shape of the contact hole, enabling the alignment film to navigate the hole's geometry properly and achieve uniform coverage across the pixel surface
2Reliability
If the contact hole diameter is increased to ensure electrical conductivity, then the electrical connection is improved, but the area where no alignment film is formed increases, causing display unevenness
Solution Approach 1:
The patent optimizes the contact hole geometry by controlling the tapered angle to be 53 degrees or less. This angular parameter allows the contact hole to maintain sufficient diameter for electrical conductivity while preventing excessive enlargement of the uncoated region, thereby avoiding display unevenness
Solution Approach 2:
The patent employs a tapered (conical) shape for the contact hole rather than a cylindrical shape. This curved geometry, defined by the tapered angle, allows the alignment film to flow into and cover the contact hole region more effectively, reducing the area without alignment film while maintaining electrical connection
Data Source
AI summary
In a high-resolution liquid crystal display device, measures against display unevenness caused by generation of a region where no alignment film is applied are provided. A liquid crystal display device includes a pixel formed between a scanning line and a video signal line. The pixel includes a TFT, a pixel electrode, and a contact hole connecting the TFT and the pixel electrode. The contact hole is formed in an insulation film formed between the pixel electrode and the TFT. Assuming that a horizontal pitch of the video signal line is ph and a horizontal diameter of the contact hole is dh, ph is 26 μm or less and s/ph is 0.73 or more where s=ph−dh. A tapered angle of a sidewall of the contact hole is 53 degrees or less. A thickness of an alignment film over the pixel electrode is 110 nm or more.