Porous Capping Layer Reduces Stress on Color Filter in TFT Array
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Solution Overview
Problem
In liquid crystal displays, the stress generated between a solid capping layer and a soft color filter leads to interface lifting and active unfilled area (AUA) deterioration due to differences in compressibility and elasticity, resulting in insufficient liquid crystal margins and image artifacts.
Innovation Solution
A thin film transistor array panel design featuring a substrate with a color filter having through holes, a capping layer with openings larger than the holes, and pixel electrodes connected through these openings, which overlap and cover the color filter, reducing stress and preventing lifting by ensuring adequate liquid crystal filling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid capping layer is formed on a soft color filter, then the color filter is protected from lifting and outgassing is blocked, but stress is generated on the capping layer and interface lifting occurs due to differences in compressibility and elasticity
Solution Approach 1:
The capping layer is designed with a porous structure containing numerous voids instead of being solid. This porous configuration reduces the compressibility difference between the capping layer and the color filter, thereby minimizing stress generation and preventing interface lifting while still maintaining protective functions.
Solution Approach 2:
The physical structure of the capping layer is changed from solid to porous, fundamentally altering its mechanical properties. This parameter change in density and compressibility allows the capping layer to better match the elastic characteristics of the color filter, resolving the stress compatibility issue.
2Reliability
If a solid capping layer is formed on a soft color filter, then the color filter is protected, but the compressibility of the contact portion is decreased, reducing liquid crystal margins and causing AUA deterioration
Solution Approach 1:
The porous structure of the capping layer restores compressibility to the contact portion, allowing adequate liquid crystal margins to be maintained. The voids in the porous structure enable the capping layer to compress appropriately, ensuring proper liquid crystal filling and preventing AUA deterioration.
3Strength
If a solid capping layer is formed, then structural support is provided, but interface lifting is generated between the capping layer and color filter
Solution Approach 1:
The porous capping layer maintains sufficient structural support through its framework while the porous structure itself accommodates dimensional changes, preventing interface lifting between the capping layer and color filter.
Data Source
AI summary
A thin film transistor array panel includes a substrate, a first thin film transistor formed on the substrate, a color filter formed on the first thin film transistor and having a through hole, a capping layer formed on the color filter and having an opening, and a pixel electrode formed on the capping layer and connected to the first thin film transistor through the through hole. The opening exposes the color filter outside the through hole.